Experimental study of nucleation and growth mechanisms of graphene synthesized by Low Pressure Chemical Vapor Deposition on copper foil

During the past 40 years, the fields of micro-electronic, energy and communication deviceshave experienced an unbelievable evolution. To continue these progresses, the development of multifunctionalmaterials presenting a broad range of properties such as high electronic and thermalconductivities, high transparency and good mechanical properties is needed. Graphene, a hexagonalarrangement of carbon atoms forming a one-atom thick planar sheet could match these demands.Several methods can be used for graphene synthesis, even though Chemical VaporDeposition (CVD) on catalytic surfaces is foreseen to be the most compatible one with industrialrequirements. Indeed, CVD graphene with an electronic conductivity of 7350 cm²V-1s-1, an electricalresistance of 30 Ω/sq and a transparency of 90% has already been obtained.1 However, these valuesare still far from the theoretical ones announced by physicists, because graphene grows as randomlyoriented domains in which scattering at the boundaries leads to lower physical properties. The CVDformation of graphene on Cu substrates has long been considered to be surface-mediated and selflimitingdue to the very low carbon solubility in Cu, thus leading to single layers formation. However,numerous studies in 2011 have shown that this is true only in a small window of deposition conditions,especially for methane partial pressure2. As a consequence, the control of graphene thickness andcrystalline uniformity on large surface areas still remains elusive and needs a better understanding ofthe mechanisms of graphene nucleation and growth.In this framework, the present study consists in synthesizing graphene on copper foils (25 mmthick, 99,999% Alfa Aesar) by CVD from methane diluted in hydrogen and argon at 0.5 Torr of totalpressure. The operating temperature was fixed at 1000°C. Scanning electron microscopy (SEM),optical microscopy and Raman spectroscopy measurements were carried out to investigate the qualityand extend of graphene sheets.