Investigation On Graphene Growth By Roll-to-roll Chemical Vapor Deposition

Graphene has rapidly become the international research frontier and hot spot since its rediscovery in 2004 because of its excellent properties and promising applications.Chemical vapor deposition(CVD)of graphene on Cu has become the main technique for the production of large-area graphene films.Both batch-to-batch(B2B)and roll-to-roll(R2R)processes can be used for mass production.Because of the simplicity of equipment,the B2B process is more commonly adopted in laboratory research,e.g.,to study the graphene growth mechanism and kinetics,to optimize the process for the improvement of film quality,to develop the growth technique for single crystal,etc..In contrast,the R2R process is more industrially preferred because it is easier to automate and more compatible with the subsequent transfer process.However,so far,the research on R2R process has mainly focused on the design of the reactor or the loading configuration,but sincerely lacking of an in-depth understanding on the growth kinetics.This thesis mainly studies the evolution process of graphene growth to optimize R2R process.Firstly,I studied the processes of R2R low pressure chemical vapor deposition(LPCVD)and R2R atmospheric pressure chemical vapor deposition(APCVD).It was found that annealing,temperature,growth atmosphere,gas flow ratio and substrate transmission speed would affect the growth of graphene.Under R2R LPCVD process,the temperature was 1030 ^oC,the gas flow ratio was 5%H₂/Ar:1%CH₄/Ar=400:100,the substrate transmission speed was 15 mm/min,continuous graphene with good quality(I_D/I_Gwas about 5%)could be prepared;graphene with coverage greater than90%could be prepared under R2R APCVD process with the temperature of 1020 ^oC,the gas flow ratio of 5%H₂/Ar:1%CH₄/Ar:Ar=30:100:50,and the substrate transmission speed of 40 mm/min.This provided support for follow-up research.Then,I investigated the evolution of graphene growth under R2R LPCVD process and revealed that the graphene domain density grown by the R2R process was larger than that by the B2B process with the same reaction parameters,which was attributed to the different reaction profiles between the two processes.Furthermore,the defective graphene could be healed with elongated reaction time.With the optimized R2R process,graphene films with quality comparable to those grown by conventional B2B process could be achieved.Finally,I studied the nucleation and evolution of graphene in R2R APCVD process.It was found that nucleation points appeared on the steps of copper foil,and Si,Ca,Mg and a large number of O impurities were introduced after annealing.These two points may be the reasons for the high coverage of multilayer graphene.In addition,I found that too high oxygen content or low temperature growth may cause graphene to be etched and damage the quality of the film.