Synthesis of Graphene Layers from Metal-Carbon Melts: Nucleation and Growth Kinetics

Doctor of Philosophy, Graduate Program in Mechanical Engineering
University of California, Riverside, December 2012
Professor Reza Abbaschian, Chairperson

A  new  method  for  growth  of  large-area  graphene,  which  can  lead  to  a  scalable  low-cost high-throughput production technology, was demonstrated. The method is based on growing of graphene films on the surface of metal-carbon melts and involves dissolving carbon in a molten metal at a specified temperature and then allowing the dissolved carbon to nucleate and grow on top  of  the  melt  at  a  lower  temperature.  The  synthesized  graphene  layers  were  subjected  to detailed  microscopic  and  Raman  spectroscopic  characterizations.  The  deconvolution  of  the Raman 2D band was used to accurately determine the number of atomic planes in the resulting graphene layers and  access  their quality. The results  indicated that the technology can provide bulk graphite films, few-layer graphene as well as high-quality single layer graphene on metals. It was also shown that upon cooling of supersaturated metal-carbon melts; graphite would also grow inside the melt either with flake or sphere morphology, depending on the solidification rate and  degree  of  supersaturation.  At  small  solidification  rates,  graphite  crystals  are  normally bounded  by  faceted  low  index  basal  and  prismatic  planes  which  grow  by  lateral  movement  of ledges  produced  by  2D-nucleation  or  dislocations.  At  higher  growth  rates,  however,  both interfaces become kinetically rough, and growth becomes limited by diffusion of carbon to the growing interface. The roughening transition from faceted to non-faceted was found to depend on the driving force and nature of growing plane. Due to high number of C-C dangling bonds in prismatic face, its roughening transition occurs at smaller driving forces. At intermediate rates, the  prismatic  interfaces  become  rough  and  grow  faster  while  the  basal  plane  is  still  faceted, leading  to  formation  of  flake  graphite.  At  higher  growth  rates,  both  interfaces  grow  with  a relatively similar rate leading to initiation of graphite sphere formation, which later grows by a multi-stage  growth  mechanism.  An  analytical  model  was  developed  to  describe  the  size  and morphology of graphite as a function of solidification parameters.