Study On The Transfer-reaction Kinetic Model And Its Enhancement Mechanism Of Graphene Chemical Vapor Depositio

As a new two-dimensional carbon nanomaterial,graphene has attracted much attention since its birth and has quickly attracted wide attention around the world.However,in the actual production of graphene,macro preparation technology has not yet made substantial progress in achieving large-scale,low-cost,high-quality and large-size industrial production,which can not meet the demand for mass production.The growth of graphene by chemical vapor deposition（CVD）method has the advantages of high quality,large area,controllable layer number and good repeatability,which can realize large-scale industrial preparation of graphene.In this paper,aiming at the problems of low deposition rate and uneven surface morphology in the process of preparing graphene by CVD method,the transfer kinetics model of graphene grown by CVD method was established by designing a special structure of CVD reactor and coupling multiple physical fields such as pressure field,temperature field and flow field.The effects of fluid flow and transfer phenomena inside the reactor on the deposition rate of graphene surface were studied as follows:（1）According to the growth mechanism of graphene on the copper substrate surface,a growth kinetics model of graphene on Cu（111）surface was established,and the energy barrier of the reaction,the influence of methane concentration on graphene growth and the thermodynamics of graphene preparation process were studied.Using thermodynamic data,according to the equilibrium component relationship,The influence of operating conditions（temperature,pressure and partial pressure ratio）on the carbon deposition rate is discussed.The research shows that:the CH_n（n=1,2,3,4）groups are involved in the formation of graphene,and reducing the dehydrogenation barrier can accelerate the growth rate of graphene.The growth process of graphene is mainly determined by the polymerization of polymer rings and the polymerization of polymer rings and carbon polymers;At the same time,no matter the high temperature and high pressure or high temperature and low pressure can promote the high-temperature decomposition reaction of CH₄,speed up the whole reaction rate;Excess hydrogen at high temperature and relatively low pressure are conducive to improving the carbon yield.When the partial pressure ratio of methane and hydrogen increases,the carbon deposition rate decreases significantly.（2）Aiming at the problems of low surface deposition rate and high energy consumption in the current growth of graphene,a transfer kinetics model of CVD reactor based on the Tesla valve structure was established.The distribution law of the flow field,pressure field and temperature field inside the Tesla valve and the influence of multi-physics coupling reaction kinetics on the graphene surface deposition rate were studied.The results showed as follows:When the intake flow rate is between 1000μl/min and 2000μl/min,the graphene surface deposition rate increases with the increase of the intake flow rate.When the intake flow rate is greater than 2000μl/min,the graphene surface deposition rate becomes gentle and has a decreasing trend,and 2000μl/min is the best intake flow rate.When the temperature range is1230K～1310K and the atmospheric pressure state,the pressure distribution inside the Tesla valve is uniform,which is conducive to the process of graphene surface vapor deposition.When the mixed gas flows forward into the Tesla valve,the graphene surface deposition rate at the deposition point B is higher than that at the deposition point A.The graphene surface deposition rate increases with the increase of temperature,and this process is limited by surface chemical reaction.When the mixed gas flows into the Tesla valve in the reverse direction,after the temperature rises,the graphene surface deposition rate at the deposition point B is higher than that at the deposition point A,which is limited by the gas phase transfer process.At both normal pressure and low pressure the pressure drop ratio Di increases as the internal temperature of the Tesla valve increases,and in the normal state,the pressure drop is more stable than the Di,and the control of the flow of fluid is more stable.The fitting equation of the pressure drop ratio for the temperature between 1230K and 1330K is Di=0.003T+0.6243;It was also found that under normal pressure conditions,the mixed gas flow rate was 2000μl/min,the mixed gas was flowing forward into the Tesla valve,and the temperature in the reactor was 1290K～1310K,the graphene surface deposition rate was up to 0.55μm/min,which was 2～3 times higher than the existing straight tube model.（3）Based on the Tesla valve structure,the experimental study was carried out,and the mixed gas flow rate under normal pressure was Under the condition of 2000μL/min,1290K～1310K,the experimental results show that:At 1310K,the graphene surface morphology is good,the roughness is low,the quality is high,and the surface deposition rate is 0.45～0.5μm/min.The relative error between the simulation results and the experimental results is only 7.2%,which shows that the simulation results are accurate and a reasonable model is established.（4）Using computational fluid dynamics（CFD）coupled with surface chemical reaction,the transfer kinetics model of graphene growth by CVD method was established based on vertical rotating reactor（VRD）.Under atmospheric pressure of 1230 K～1330 K,The effects of gas temperature,intake speed,substrate speed and material（CH₄/H₂）ratio on the deposition rate of graphene surface in VRD reactor were investigated.The results show that the ideal growth conditions of graphene prepared by CVD method in VRD reactor are as follows:T=1310K,inlet speed is 470000μl/min,substrate speed is 300 rpm,and H₂flow rate is 75 sccm.At the same time,molecular dynamics（MD）and microscopic transfer phenomenon were used to verify that the growth mechanism of graphene in VRD reactor was affected by the deposition rate of graphene surface.The results show that the nucleation density of graphene is controlled by the graphene surface deposition rate.When the reaction temperature was from 1290 K to 1310 K,the number of carbon atoms produced by gas pyrolysis increased,and the deposition rate of graphene surface accelerated.When the temperature is 1310 K and the carbon deposition rate is5 ps^-1,the number of five-and six-membered carbon rings on the surface of copper substrate is more,and the deposited graphene is of good quality and high surface density.When the carbon deposition rate is less than 5 ps^-1,the number of stable carbon rings increase with the increase of carbon deposition rate,and the quality of graphene is continuously improved.When the carbon deposition rate increases to 10 ps^-1,the number of stable carbon rings decreases and the quality of graphene decreases,which is not conducive to the surface growth of graphene.Therefore,the graphene surface deposition rate can control the nucleation density of graphene,but too high or too low the surface deposition rate is not conducive to the preparation of uniform graphene.