AsianScientist (Aug. 2, 2017) – A team of scientists from Korea and China have developed a method to synthesize large sheets of monolayer single-crystal graphene. They report their findings in the journal Science Bulletin.
Boasting high conductivity, strength and flexibility, graphene was proposed as one of the most likely substitutes for silicon and other materials. Polycrystalline graphene is formed by randomly oriented graphene islands, which decrease its quality. On the other hand, a honeycomb-shaped monolayer of carbon atoms, uniform throughout the whole material, offers exceptional properties to single-crystal graphene.
Currently, scientists can grow meter-sized polycrystalline graphene and smaller single-crystal graphene, ranging from 0.01 mm2 to a few square centimeters. The synthesis of large single-crystal graphene at a low cost has been considered a critical goal of graphene synthesis.
In this study, a team of researchers led by Professor Ding Feng and Professor Rodney Ruoff at the Center for Multidimensional Carbon Materials within the Institute for Basic Science reported the synthesis of a large sheet of monolayer single-crystal graphene.
The researchers grew graphene on the surface of a 5 × 50 cm2 copper foil, which was transformed into a single-crystal copper foil by heating to approximately 1,030 degrees Celcius. A temperature slope from hot to cold moved the so-called grain boundary onward, creating a perfect single crystal. During the heating and cooling treatment, copper atoms migrated inside the material, arranging into an ordered structure with fewer defects.
Then, using another technique called chemical vapor deposition, millions of parallel graphene islands were formed on the copper foil surface. As more carbon atoms deposit on the foil, the islands kept on growing until they coalesced and formed a very-close-to-perfect single-crystal graphene layer that covered the entire available surface.
“The secret to obtaining single-crystal graphene of a very large size is to have a perfect single crystal copper as a base to start with. Large single-crystal copper foils are not available in the market, so labs must build it with their own means,” explained Ding.
The team’s findings allow a leap forward in graphene production, advancing from a technique that synthesizes a few square centimeters of single-crystal graphene in a couple of hours, to an optimized method that allows the creation of an almost-perfect (> 99.9 percent aligned) 5 × 50 cm2 single-crystal graphene in just 20 minutes.
Moreover, the low production costs, comparable to commercially available lower quality polycrystalline graphene films, could expand its usability. The method is expected to stimulate further fundamental work on graphene and related materials, including large scale folding of graphene sheets, similar to paper, creating origami-like or kirigami-like shapes, which could be applied to future flexible circuits.
“The dream of many scientists is to make graphene the material of the future, to replace silicon,” Ding said. “We are exploring the best material on which to grow graphene and using copper as a substrate for other interesting 2D materials.”
The article can be found at: Xu et al. (2017) Ultrafast Epitaxial Growth of Meter-sized Single-crystal Graphene on Industrial Cu Foil.
Source: Institute for Basic Science.
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