Influence Factors And Characterization Of Graphene Films Prepared By Atmospheric Pressure Chemical Vapor Deposition (APCVD)

Due to its high performance in mechanics,optics and electrobics,graphene film has a great potential prospect in many fields.However,low cost preparation of high quality graphene film is still a key bottleneck for its extensive application.In this paper graphene thin films was deposited onto polycrystaline copper foil by Atmospheric Pressure C hemical Vapor Deposition(APCVD).The Raman spectra,morphology,sheet resistance and light transmittance of graphene films were characterized.The influence on the properties of graphene films were studied by controlling the processing parameters,such as heat treatment of copper foil substrate,using different methane flow for stepwise growth,and artificial introduction of nucleation seeds.The following main conclusions can be drawn.1)Few-layers graphene films(FG)can be prepared by low-cost atmospheric pressure chemical vapor deposition(APCVD).With methane flow percentage increasing from,the ID/IG ratio of graphene increased from 0.18 to 0.35,and its defect also showed an increasing trend.Its sheet resistance also showed a monotonically rising trend,rom 2118?·?-1 to 5870?·?-1.2)The grain size of a cooper foil substrate can be changed from less than 60 ?m to more than 80 ?m using annealing tratrment.Accordingly,.the ID/IG ratio decreased(decreased from 0.61 to 0.23)with the longer heat treatment period and the higher heat treatment temperature of copper foil.At the same time,the sheet resistance of graphene also showed a decreasing trend from 1.708 k?·?-1 to 0.902 k?·?-1.Obviously,heat treatment of copper foil is beneficial to reduce its grain boundary density by coarsing its grain size.The improvement of the conductivity of a graphene is responsible for lowering copper grain boundary density and other defects,which causes the carrier scattering effect.3)During preparing the graphene film by two-step method in this study,the grephene crystal nucleation density can be controlled by the flow rate of carbon source and deposition time in the first step.It decreased from 0.453/?m2 to 0.209/?m2,when methane gas flow droping frrom 45 sccm to 5 sccm,and deposition time was 30 s.When a high methane flow 45 sccm is used in the first step,the ID/IG ratio of graphne film decreasd with shortening deposition time.During the second growing process,part of graphene would grow around the crystal nucleus formed in the fisrt step,and then connect with the graphene grew from nearby crystal nucleus.4)The copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate)crystalline powder was introduced as the initial nucleation seed for preparing graphene.Carbon atom aggregated preferly at regions with high unbalanced defect free energy such as the seed region and the grain boundary regions.Comparing with the untreated copper foil,the ID/IG ratio of graphne film can be lowed from 0.41 to 0.33 using a copper foil previously trated by copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate).It shows that the introduction of a certain amount of seeds to control the nucleation density of graphene,to a certain extent,will improve the quality of graphene.