A team of researchers from China has designed a new growth method that produces smooth and pristine graphene. Using a carefully engineered substrate, the researchers can grow high-quality graphene free of wrinkles that often form during manufacture. The team reports that the super-smooth graphene has shown improved electrical properties over rumpled graphene grown by the usual methods.
Existing methods usually use copper foil as a growth substrate to form a sheet of graphene. However, the research team hypothesized that a mismatch in material properties between between graphene and the copper growth substrate may be the cause of wrinkling that often damage the resulting graphene's properties. Graphene and the form of copper usually used as substrate expand at different rates at a given temperature, leading to mechanical strain and causing wrinkling. So, the team searched for copper substrates with a crystalline structure that’s a better match.
They report that graphene grown on a thin film of Cu(111) is perfectly smooth. What’s more, its electron mobility, a measure of how easily current moves through a material, is 11,000 cm2 per V-second. This ranks among the highest levels ever measured for graphene grown over large areas using practical methods. The team was able to grow Cu(111) films with the proper crystal structure using 10-cm sapphire wafers as a support. The copper-sapphire wafers can be reused after the graphene is removed.
The team says this method is compatible with the technology used by the semiconductor industry. The next step is manufacturing. “We are trying to realize the mass production of this wrinkle-free, single-crystal graphene,” the researchers say.