Preparation And Application Of Graphene By Chemical Vapor Deposition Method

With excellent properties,graphene has become one of the most popular materials in the research field.The synthesis and applications of graphene have increasingly come into focus.Copper based Chemical Vapor deposition(CVD)is the most widespread and reliable method for preparing graphene,yet preparation of qualified graphene remains challenging.In the meantime,despite its superb properties and is widely used in research field,its practical applications have been limited.In this thesis,we carry out the research from preparation of CVD graphene.In addition,the anticorrosion behavior of few-layer graphene(FLG)for copper is studied and FLG is also applied to organic light emitting diodes(OLED).In the aspect of graphene growth control,following systematic studies are carried out: 1.The influence of ratio of H2/CH4 on graphene is investigated.The growth rate of graphene is found to be fast at a specific flow rate of H2 and can be optimized by carefully tuning H2 flow and keep other parameters unchanged.2.The rules of how graphene growth changes with various growth temperature and growth time are probed.It is found that the growth rate of graphene accelerates with the higher temperature,that is,the existence of a bare surface is necessary for the catalytic decomposition of CH4 and the promotion of graphene growth on the copper foil surface.3.The influence of different copper vapor partial pressure(Pcu)and copper vapor concentration(CCu)and on graphene synthesis is investigated.The functions of Pcu varies with carrier gas and CCu varies with system pressure are calculated with carefully designed experiments.With higher CCu comes higher graphene growth rate and nucleation density.4.After combining all the growth parameters and experiences,graphene single crystal up to~1.5mm is synthesized.Also,the successful preparation of ~50-70 μm regular compact hexagon single crystal graphene and onion-like graphene nanoribbons is conduct.Furthermore,graphene with different layers of about ~200 μm in size is prepared.In aspect of application of FLG on the corrosion behavior of copper foil,FLG proves to be applicable as anticorrosion coating for copper for as long as six years.1.Firstly,by employing optical microscopy(OM),Scanning electron microscope(SEM),and Raman spectroscopy,it is found FLG has no cracks in SEM image or defective peaks in Raman spectroscopy and that the steps on the copper foil are still visible after six years in atmosphere.While the single layer graphene(SLG)can not protect the underlying copper foil,the copper foils become darker with the steps bunches disappearing.Also,the graphene cracks is clear in OM and SEM image,and the defective D peak in Raman spectroscopy is obvious.2.Secondly,the surface potentials of fresh,six-year aged FLG and SLG are measured by scanning Kelvin probe microscope(SKPM).After six years in air,the surface potentials of SLG tend to be consistent with that of bare copper.At the junction of SLG and copper,the surface potential is smallest with the most serious corrosion.However,the surface potential difference is not smeared for aged FLG and copper.The copper steps is still extinct and not corroded.3.Thirdly,Raman spectroscopy is employed to identify the grain boundaries(GBs)of isotopic FLG.GBs of FLG are misaligned so the water molecule can’t contact the copper surface and will corrode the copper through the SLG GBs.To be a step further,the energy barrier of water molecule passing through SLG GB and jumping between two layers of FLG is calculated.It is found that the energy of passing two adjacent carbon atoms(0.25 nm)defect is 0.06 e V,it can be realized only by fluctuation of room temperature.While the energy required to diffuse through the van der Waals gap between two graphene layers in a FLG system is two orders of magnitude higher.4.Finally,other features of FLG anticorrosion film is analyzed.It will also protect the substrate when it’s transferred.A small scratch will not exacerbate its protection performance at other regions and it’ll remain effective in higher temperature.In the aspect of the application of graphene as the anode of OLED,graphene anode and graphene/ITO anode OLED devices are prepared by wet transfer method.The luminance of the device with graphene/ITO anode is 20520cd/m2,which exceeds the maximum luminance of the pure ITO anode device.The power efficiency is 3.87lm/w and the current efficiency is 11 cd/A for it.And the luminance of the device with graphene anode is 6805cd/m2,qualified for practical application.The method of using graphene as cathode or as cathode and anode to make complete transparent OLED devices is also proposed.To sum up,the study on the synthesis and application of graphene is of great significance.The controllable growth of graphene can help to further understand its growth mechanism,and can lead to the development of graphene materials in other fields.The study of graphene at atomic-scale anticorrosion film will not exacerbate the material’s optical and electrical performance,and further expand the graphene to other related fields.The basis of graphene—carbon atom is easily available and with the development of technology,the cost to synthesize graphene will be further reduced.The study of high performance graphene based OLED will bring new development to the displaying field.