Growth And Characterization Of Large Size Single Crystal Graphene By Seed Induction Method

Graphene is a kind of two-dimensional crystalline new material,which is composed of carbon atoms in sp2 hybridized honeycomb lattice struct·re.This unique structure determines that graphene has excellent electrical,mechanical and thermal properties,and has great application potential in new micro-nano electronic devices and weak photodetectors devices.Currently,a variety of graphene preparation methods have been developed.Among them,chemical vapor deposition(CVD)method can prepare high quality and large area graphene,and is the most promising method for industrial preparation of graphene.The growth of graphene is a typical self-reconfiguration process of non-correlated nucleation points.In the process of CVD growth,crystal domains would be connected to each other to a large extent to form graphene polycrystalline films after the nucleation of graphene.The grain boundaries in the polycrystalline films will hinder the electron transport,reduce the electron mobility of graphene,and affect the performance of its electrical properties.Therefore,it is necessary for us to develop a new method and technology to prepare large-size and high-quality single-crystal grapheneThe preparation of large-size single-crystal graphene mainly consists of two ideas:the seamless connection of multi-point nucleation crystal domains and the growth of single-point nucleation single crystal domains.In this paper,we mainly focus on the idea of preparing graphene by single point nucleation.Combined with the habit that graphene is easier to nucleate at the step and the creativity of seed crystal inducing the growth of bulk single crystal,the experimental scheme of seed crystal inducing the growth of large size single crystal graphene was proposed.By artificially introducing seed crystals on the growth substrate to induce the nucleation and growth of graphene,the localized growth of graphene is not only realized,but also the spontaneous nucleation of graphene is inhibited to a certain extent,and the growth rate of graphene is also improved.Finally,a local carbon source method was designed and tried to grow large size graphene and the growing graphene was characterized.The main results are as follows1.Study on CuO seed crystals induced growth of grapheneThe experimental scheme of CuO seed crystal induced graphene growth was designed.It was observed that the nucleation of graphene on Cu(111)substrate was mainly centered on CuO nanoparticles at the initial stage of growth,and the presence of CuO nanoparticles could reduce the nucleation density of graphene to some extent.After pretreatment of copper foil,it was found that the nucleation density of graphene was significantly lower than that of untreated samples.the nucleation density without pretreatment of>60/mm2 was reduced to 1/mm2 after pretreatment.And the crystal domain size was also greatly increased to sub-millimeter level.It was closely related to the introduction of CuO seed crystals.2.Study on h-BN seed crystals induced growth of large size single crystal grapheneAn experimental scheme for h-BN seed crystal induced growth of large size single crystal graphene was designed.Since h-BN is similar to the structure of graphene crystal and the lattice mismatch rate is very low,h-BN is selected as seed crystal to induce growth.Through in situ growth observation by transmission electron microscope,it has been proved that graphene can be grown laterally around the h-BN seed crystal edge.The theoretical studies shown that activated carbon atoms are more likely to adsorb at the h-BN seed crystal edges,thus promoting the nucleation and growth of graphene around the h-BN seed crystal edges.Combined with the catalytic properties of Cu substrates and the induction effect of h-BN seed crystals,it was observed that the growth rate of graphene induced by seed crystals on Cu(111)substrates was much higher than that of graphene grown by spontaneous nucleation.Finally,the graphene single crystal sized 3 mm was prepared by adjusting the substrate roughness,seed crystal concentration,growth time and other conditions.Meanwhile,it was also found that h-BN would be gradually etched by hydrogen as the growth went on,and the carbon active group would fill the vacancy.Finally,perfect graphene single crystal could be prepared by this method.This work shows that the h-BN seed crystal induction method has advantages in improving the growth rate of graphene and reducing the domain density of graphene crystal,which is conducive to the development of the preparation of other two-dimensional new materials.3.Study on the growth of graphene by local carbon source methodIn order to realize the fixed-point single nucleation growth of large size single crystal graphene,the local carbon source method was used to grow graphene.The key factors conducive to the growth of graphene were studied by optimizing the experimental conditions.Cu-Ni alloy substrates were prepared,the effects of electroplating voltage,electroplating time and annealing time on the alloy were discussed,and the optimum conditions for Cu-Ni alloy preparation in constant current mode were determined.The effect of annealing of copper foil before electroplating on the morphology of graphene was compared.It was found that CVD at atmospheric pressure was more conducive to the fixed-point nucleation of graphene than that at low pressure CVD.Finally,the growth of graphene domains in a fixed region was realized.