Oriented Growth Of Graphene Films By Chemical Vapor Deposition

Graphene,a two-dimensional material with a honeycomb structure made of carbon atoms,has attracted broad attention due to its unique and remarkable physical properties.Among various graphene fabrication methods,chemical vapor deposition(CVD)of graphene on single crystal metal substrates is currently considered to be the most promising method to obtain the high-quality graphene.The Cu(111)crystal plane is one of the most suitable substrates for the preparation of large-area single crystal graphene(SCG)due to its low lattice mismatch with graphene and hence to achieve oriented growth of graphene crystal domains.However,the orientation of graphene on Cu single crystals has not been fully understood.Moreover,the report about the orientation of graphene on polycrystalline Cu foil is rarely mentioned.Thus,the investigation of the orientation of graphene on Cu substrate is beneficial for further understanding and controlling the graphene growth during CVD process.In this work,a polycrystalline copper film was prepared by thermal evaporation on quartz substrate,and regular graphene crystal domains were grown on this substrate via low-pressure CVD,the orientation regulation phenomenon between Cu substrate and as-grown graphene was found.The relationship between the physical properties of Cu film and the fabrication parameters were studied in detail.It is found that when the contact temperature between the evaporating Cu atoms and the substrate is high enough,the Cu film will maintain the Cu(111)as the main crystal phase with a typical polycrystalline morphology,regardless of evaporation rate,evaporation material and evaporation thickness.The orientation of the Cu crystal domains was characterized by electron backscatter diffraction(EBSD).The misorientation of Cu domains and asgrown graphene were associated,and there is a congruent relationship between them,which indicates that the orientation of graphene is regulated by the Cu substrate,and based on that to reveal the specific orientation of graphene grown on Cu substrate.In this work,the specific orientation of graphene crystal domains grown on different Cu substrates based on EBSD characterization.Based on the orientation data of Cu substrate characterized by EBSD,the three-dimensional atomic arrangement and surface atomic arrangement of each Cu domain were obtained by using software modeling,the lattice orientation of each Cu domain is obtained.Then the specific orientation of the graphene and the rotation angle between graphene and Cu substrate were determined by combining the orientation of the copper lattice with as-grown graphene.It was also found that the same orientation relationship was existed for the graphene grown on different crystal surfaces of traditional polycrystalline copper foil.Our research contributes to the understanding of the growth of graphene on metal substrates,which paved the way for the seamless stitching of SCG domains,and played a crucial role in the controlled growth of large area SCG film in the future.The influence of the grain boundary of graphene on the macroscopic physical properties of graphene film could also be explored.Furthermore,polycrystalline copper foils with different crystal domain size were also prepared by adjusting the atmosphere during the CVD heating process.And the influence of graphene grain boundary caused by Cu grain boundary on the electrical properties of graphene was exported.For the graphene domains grown on the same Cu(111)domain,graphene grain boundary will not exist thanks to the oriented growth.While graphene crystal boundary will form at the Cu grain boundaries due to the orientation regulation of the substrate on the grown graphene.By transferring as-grown graphene to PET substrate,we found that due to the area of Cu grain boundary was too small comparing with the size of graphene,the influence of Cu grain boundary on the mobility carriers and resistance of as-grown graphene was not found.Our study shows that the grain boundary in traditional copper foil has little influence on the macroscopic physical properties of as-grown graphene after transfer,which provides help for the improvement of the physical properties of the graphene film after transfer.