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 devices have experienced an unbelievable evolution. To continue these progresses, the development of multifunctional materials presenting a broad range of properties such as high electronic and thermal conductivities, high transparency and good mechanical properties is needed. Graphene, a hexagonal arrangement 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 Vapor Deposition (CVD) on catalytic surfaces is foreseen to be the most compatible one with industrial requirements. Indeed, CVD graphene with an electronic conductivity of 7350 cm²V-1s-1, an electrical resistance of 30 Ω/sq and a transparency of 90% has already been obtained.1 However, these values are still far from the theoretical ones announced by physicists, because graphene grows as randomly oriented domains in which scattering at the boundaries leads to lower physical properties. The CVD formation of graphene on Cu substrates has long been considered to be surface-mediated and selflimiting due 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 and crystalline uniformity on large surface areas still remains elusive and needs a better understanding of the mechanisms of graphene nucleation and growth. In this framework, the present study consists in synthesizing graphene on copper foils (25 mm thick, 99,999% Alfa Aesar) by CVD from methane diluted in hydrogen and argon at 0.5 Torr of total pressure. The operating temperature was fixed at 1000°C. Scanning electron microscopy (SEM), optical microscopy and Raman spectroscopy measurements were carried out to investigate the quality and extend of graphene sheets