Controlled growth of high-quality graphene using hot-filament chemical vapor deposition

High-quality graphene was grown on polycrystalline copper (Cu) foils (1 cm x 1 cm) using hot-filament chemical vapor deposition method. The role of process parameters such as gas flow rates (methane and hydrogen), growth temperatures (filament and substrate) and durations on the growth of graphene was studied. The process parameters were also optimized to grow monolayer, bilayer and multilayer graphene in a controlled manner, and a growth mechanism was deduced from the experimental results. The presence of graphene on Cu foils was confirmed using X-ray photoelectron spectroscopy, microRaman spectroscopy, field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. FESEM micrographs clearly showed that the graphene starts nucleating as hexagonal islands and later evolves as dendritic lobe-shaped islands with an increase in supersaturation. The TEM images substantiate the growth of monolayer, bilayer and multilayer graphene. The I-2D/I-G ratio = 2 confirmed the presence of the monolayer graphene and the absence of `D' peak in the Raman spectrum indicated the high purity of graphene grown on Cu foils. These results also show that the polycrystalline copper foil morphology has negligible effect on the growth of monolayer graphene