Effect of hydrogen flow during cooling phase to achieve uniform and repeatable growth of bilayer graphene on copper foils over large area

The growth of single-layer graphene on copper foil by chemical vapor deposition (CVD) method has been investigated extensively by several groups, however, achieving the same for the bilayer graphene, using a fast and reproducible process, is proven to be difficult and most of the efforts in this direction so far have been on controlling the nucleation phase during active growth regime. In this article we show that by regulating the gases introduced during the cooling phase, uniform and continuous growth of both the single and bilayer graphene can be obtained on copper foils with growth phase duration reduced to 3 min (i.e., 5-60 times faster than previous methods). We demonstrated growth of bilayer graphene on 30 × 30 cm copper foils. We show that the use of vacuum cooling enhanced the growth of single-layer graphene while the introduction of hydrogen gas during the cooling phase promoted the growth of bilayer graphene. We explain observed results elucidating a crucial role of hydrogen leading to a growth of bilayer graphene. The characterization of single and bilayer graphene have been supported by extensive statistical analysis of Raman spectroscopy, selected area electron diffraction measurements as well as fabrication of graphene field effect transistors.