Investigation of monolayer-formation time for the synthesis of graphene   on copper/nickel/silicon using very-low pressure pulses of methane
  Chemical Vapor Deposition (CVD) of graphene on copper is one of the most efficient technologies for producing high quality graphene for large areas. Nevertheless, still high pressures and big quantities of precursor gas are currently required. The objective of this work is to deposit graphene using the monolayer-formation-time concept (t) from the kinetic theory of gases, which leads to an economization of the precursor gas, a minimization of the process pressure and the time needed to grow a graphene monolayer. Our process has been designed taking into account the dependence of t on the pressure, the mass particle of the gas, the sticking coefficient, and the growth temperature. Thus, with this alternative method, based on CVD but using very-low pressure instant pulses of precursor gas (~10^-4 Pa), we have reduced the deposition time to the order of 10 s. We carried out the processes at temperatures below 1000 Grad Celsius with methane (CH4) as a precursor gas under High Vacuum (HV) conditions. After Raman spectroscopy and mapping, and Scanning Electron Microscopy (SEM) characterization of the samples, the results point to the formation of high quality monolayer graphene on sputtered copper and silicon substrates covering domain areas of 10^4 micron^2. 
V-M. Freire, A. Ramirez, E. Pascual, E. Bertran, and J-L. Andujar
cond-mat.mtrl-sci