Ethanol-CVD Growth of Sub-mm Single-Crystal Graphene on Flat Cu Surfaces

High-quality graphene can be produced in large scale by chemical vapor deposition (CVD). Ethanol is emerging as a versatile carbon source alternative to methane for the growth of graphene on a copper (Cu) foil catalyst. To date, rigorous studies of the ethanol-based process still lack, especially concerning the first stages of the growth, which ultimately determines graphene's properties, such as defect density and crystal size, and performance, such as electrical conductance and mechanical strength. In particular, so far the growth of isolated graphene grains by ethanol-CVD has been achieved only on preoxidized Cu foils folded in enclosures, in an attempt to limit the partial pressure of the precursor, and thus the nucleation rate. We systematically explored the process parameters of ethanol-CVD to obtain full control over the nucleation rate, grain size, and crystallinity of graphene on flat Cu foils, which are of interest for any realistic production in large scale. To limit the nucleation density and increase the grain size, preoxidized Cu foils (250 °C in air) were used as substrates, and the process parameters were thoroughly investigated and tuned. Ultimately, at an ethanol vapor flow of 1.5 × 10^-3 sccm the nucleation density reduced to less than 3 nuclei/mm² and isolated single-crystal grains grew with a lateral size above 500 μm. When transferred onto Si/SiO₂ substrates, these grains showed field-effect mobility beyond 1300 cm²/(V s). Our results provide a step closer towards an affordable commercialization of electronic-grade, large-area graphene.