Comprehensive nucleation mechanisms of quasi-monolayer graphene grown on Cu by chemical vapor deposition

• Suppressed nucleation densities by (NH4)2(SO4)2 etching and hydrogen annealing.
• Domain sizes were increased at the same time.
• Increased domain sizes by modulating the gas flow rate of CH4.
• We found the nucleation is quite sensitive of temperature.
• There is a critical point of temperature, which is 1030 °C in this work.

We propose a detailed mechanism of suppressing the nucleation density of large-scale graphene on Cu foil during the chemical vapor deposition. Here, quasi-monolayer (discontinuous) graphene with an individual domain was grown at a series of temperatures ranging from 950 to 1060 °C. The nucleation was investigated via modulating the surface morphology of Cu foil by chemical etching, pre-annealing and adjusting the gas flow ratio of CH4 to H2. It revealed that proper chemical etching and H2 pre-annealing could efficiently improve the morphological performance of Cu substrates and suppress the nucleation density. Furthermore, the nucleation greatly depends on the growth temperature. As the temperature increased from 960 to 1060 °C, nuclei densities decreased gradually while domain sizes increased. Another critical factor is the gas flow rate of CH4. It indicates that lower gas flow rates are benefit for lower nuclei densities and larger domain sizes of graphene with a steady H2 gas flow rate. Moreover, we find the most proper temperature for the growth of CVD-graphene is about 1030 °C in this work.