Study On A New Method For Induced Growth Of Graphene By Using Heterogenous "Point Seed"

After the report of graphene in 2004,the unique properties attracted tremendous attention in scientific research communities.This is a hexagonal honey-comb-like single atomic layer of carbon.The unique two-dimensional planar structure provides it many excellent electrical properties.At present,the chemical vapor deposition method is the best way to achieve the preparation of high-quality large-area graphene,and great progress has been made in the preparation of graphene on many substrates,especially with copper as the most widely used substrate.However,conventional CVD method is a non-associated nucleation site on the copper foil,which spontaneously nucleates and grows graphene.The prepared product is a polycrystalline graphene with a large number of grain boundaries,which affect the excellent electrical performance of graphene,and limits the application of graphene in the field of microelectronic devices.From this point of view,in this work,single crystallization of the copper substrate to achieve the preparation of a single crystallographic graphene was studied.The nucleation sites were introduced on the copper substrate in advance to suppress the formation of non-associated nucleation sites.The main research contents and experimental conclusions of this dissertation are as follows:1.Effect of CuO nanocrystals on the nucleation and growth of graphene on substrateConsidering the correlation of the copper substrate,CuO nanocrystals were designed and prepared as a "point seed" for inducing graphene growth.In this work,the CuO nanocrystals were formed as a "point seed" after oxidation and hydrogen etching of the copper substrate.The effects of different oxidation levels on the surface morphology of the copper substrate were investigated.Results showed that the oxide thickness of the Cu surface not only could significantly affect the formation and the number of CuO nanocrystals,but also could affect the roughness of the copper substrate surface,and directly affect the quality of the graphene.It was obtained that when annealing the copper substrate at 300 ℃ for 30mins with flow ratio of 64:1(Ar:O2),the copper substrate showed the lowest roughness and the least amount of CuO nanocrystals after hydrogen etching(21 sccm at 1035 ℃).Graphene was grown on the copper substrate prepared under this condition,and the larger size of single crystal graphene was obtained,the domain size of the single crystal could reach～3 μm.2.Growth of graphene induced by hexagonal boron nitrideHexagonal boron nitride was introduced on the surface of the copper substrate as a nucleation site for the single crystal graphene growth.The graphene was designed to continuously grow along the outer edge of the hexagonal boron nitride by controlling the process conditions.Taking advantage of the introduction of BN particles,the technical defects of the conventional CVD method could be avioded and large-size single crystal graphene were obtained.Under the same growth conditions(temperature 1035 C,time lmin,methane flow 4sccm),boron nitride as the nucleated center of graphene,its single crystal domain size is nearly 5 times that of the random nucleation growth of graphene.The results show that the growth rate of graphene can be obviously improved by the introduction of hexagonal boron nitride.3.Controlled growth of single crystal orientation grapheneIn order to obtain a single crystal orientation of graphene domains,a single crystal experiment was performed on a polycrystalline copper substrate.Through the surface oxidation(200℃,30min)and high temperature annealing(1070℃,60min)of the copper substrate,the commercial polycrystalline copper foil was transformed into a single-oriented single crystal copper,fully(111)oriented single crystal copper foil was obtained for single domain graphene growth,and the size of the as-grown graphene reached to～416.70 μm.