Correlating nucleation density with heating ramp rates in continuous graphene film formation

Graphene films with different nucleation densities were successfully grown on Cu foils using an atmospheric pressure chemical vapor deposition (APCVD) method. We investigated the effect of heating ramp rate on graphene growth, which is critical to the control of both the domain density and the defects density in further synthesized graphene film. Density of graphene domains was reduced with a decrease in ramp rate; heating Cu foil at a lower rate produced flat and smooth surface with larger Cu grains. These surface roughness and grain size-heating rate association were confirmed by atomic force microscope and electron backscatter diffraction analysis. By comparing micro Raman mappings of the graphene films grown with different ramp rates, we found that the number of layers, defect density, and uniformity of as-grown graphene films were strongly dependent on heating ramp rate. With these observations, we demonstrate the growth mechanism of graphene films as a function of the heating ramp rates.