Preparation And Characterization Of Large-area Single Crystal Graphene

Graphene,a single atomic layer,is a kind of two-dimensional materials which is composed of hexagonal honeycomb carbon atoms with sp²-hybridized structure.Because of its unique band structure and physical properties,it has been favored by scientists from various countries since it was discovered in 2004.Graphene is the world's thinnest and most hard nano-materials at present,has excellent light transmittance,mechanical properties,and thermal conductivity,but also has high carrier mobility,quantum Hall effect and bipolar field effect.It makes graphene have a good application prospect in the field of effect transistors,flexible display,energy storage devices,the super capacitors,even in the field of superconducting.The preparation of large-area single crystal graphene is the fundamental and prerequisite for the research and application of all its properties.The relationship between the roughness of copper substrate and the defect density of graphene which was obtained by plasma enhanced chemical vapor deposition is investigated.In this work,the study of the copper substrate's roughness effect on graphene defects which fabricated by chemical vapor deposition and different experimental parameters in the process of graphene growth is investigated.The copper substrate with different roughness could be obtained by using sandpaper,high-temperature annealing,acid etching processing method,which will ensure that all the samples grow under the same conditions.When methane as the carbon source,the RF power is100W,the temperature is 700?,graphene could be obtained with mixed gas?CH₄/H₂/Ar?into 22sccm for 90min.And the samples morphology and quality of graphene preparation was characterized by SEM and Raman spectroscopy,respectively.Therefore,the relationship of graphene defect density and surface roughness was obtained.In addition,the above experimental phenomena were simulated by Materials Studio software.We found that the roughness of substrate is the most affected when the roughness of substrate is the same as that of graphene.Moreover,with the increase of the roughness,the density of graphene defects on the substrate increases first and then decreases.The size of graphene film 10cm*10cm was obtained.Copper foil surface is almost completely covered with graphene and most of the region is a single,there only a small area of the bilayer.Graphene coverage rate on copper surface reached100%,which accounted for more than 95%single.Then,the coverage,lattice integrity and number of graphene layer on the surface of copper foil were analyzed by STM,SEM and Raman spectrometer.The results showed that the graphene obtained was not only single layer structure,but also had perfect honeycomb structure.In addition,the obtained graphene films have been successfully transferred to the insulating substrate PVC,and the transmittance and other physical properties of the films have been verified.The sticking and stacking of graphene are realized by chemical vapor deposition.The morphology,structure and number of graphene layer were characterized and analyzed by optical microscope,SEM and AFM.The results show that fractal graphene and polygon of graphene on the surface of copper foil,the stacking of fractal and polygon graphene could be realized by adjusting the experimental parameters.According to the AFM images of graphene which transferred to SiO₂,we observed the graphene stacking structure was at least 3.In addition,not only the stacking and sticking were observed,but the sticking of the stacked graphene was also observed.Using a variety of testing methods,such as optical microscopy,scanning electron microscopy?SEM?,atomic force microscopy?AFM?,scanning tunneling microscopy?STM?,X ray photoelectron spectroscopy?XPS?,transmission electron microscopy?TEM?,Raman spectroscopy,different graphene morphologies,layers,structures,defects,and stacking manners are the characterized and analyzed.In addition,the results of experiments are explained and analyzed.