The technque developed by Prof Feng Ding and Prof Rodney Ruoff at the Centre for Multidimensional Carbon Materials within the Institute for Basic Science (IBS) at the university uses a single crystal copper foil as a substrate with graphene grown on top using chemical vapour deposition (CVD). This produces a crystal of graphene that is 99.9% perfect measuring 5 x 50cm in just 20 minutes.
Previous synthesis techniques have produced much smaller single crystals measuring a few cm.
The key is the single crystal copper substrate, which is created by heating copper foil to 1030 ºC. A temperature slope from hot to cold moves the grain boundary in the copper foil as it heats, creating a perfect single crystal.
“The secret to obtain single-crystal graphene of very large size, is to have a perfect single crystal copper as a base to start with. Large single-crystal copper foil is not available in the market, so labs must build it with their own means,” said Feng Ding, group leader at the Center for Multidimensional Carbon Materials. “The dream of many scientists is to make it the material of the future, to replace silicon,” said Ding. “Now we are exploring which is the best material to grow graphene on top and how to use copper as a substrate for other interesting 2D materials.”
CVD is then used to deposit carbon atoms on the substrate, forming isalnds of graphene. The islands keep growing until they coalesce and form a near perfect single-crystal graphene layer that covering the entire available surface.
The team had to consider key technical challenges, from the preparation of single-crystal copper foil in a very large area to maintaining a high degree of alignment of the graphene islands following the nucleation and growth as well as seamlessly stitching the graphene islands into a single crystal through further growth. The degree of the misaligned graphene islands is less than 0.1%, thus great reduced defects and grain boundaries in the products.
The current result was limited only by the size of the copper foil and, in principle, both the size of the copper foil and graphene film could perhaps be unlimited say the researchers. In addition, considering the very short time of graphene synthesis of 20 minutes and the relatively low-cost experimental setup, the price of a near single-crystal graphene sheet could be close to that of current polycrystalline graphene films.