For the first time, American scientists have successfully synthesized graphene nanoribbons one after another on a metal surface, creating a unique "onion ring" structure of graphene in a furnace. According to a recent study published in the *Journal of the American Chemical Society*, this novel form of graphene could revolutionize applications in lithium-ion batteries and next-generation electronic devices.
James Tour, a physicist at Rice University and one of the lead researchers, explained that typically, graphene grown via chemical vapor deposition starts with a small seed—like a tiny bump or dust particle on copper or another metal surface. During the nucleation phase, carbon atoms attach to the seed, and then other atoms begin to form a mesh-like structure, resembling a wire.
To understand how the first ring of graphene forms under high pressure and in a hydrogen-rich environment, the team conducted a series of experiments. They discovered that when hydrogen is present, the edges of rapidly growing graphene flakes become hydrogenated, turning into active nucleation sites. These edges allow carbon atoms to be incorporated beneath the graphene layer, initiating the growth of a new sheet underneath. However, as the top layer grows quickly, it blocks the flow of carbon atoms to the lower layer, halting its growth and resulting in a single graphene ring. This cycle repeats, leading to a multilayered "onion ring" structure.
Tour described the process: “The mechanism relies on the topmost graphene layer preventing carbon atoms from reaching the bottom. What we end up with is a laminated, multi-layered single-crystal graphene 'onion ring.'â€
He added, “Normally, if you cut large pieces, you get nanobelts. But by starting from scratch, we can grow nanoribbons with controlled edges. The atomic structure of the edges determines the electrical properties of graphene. The hexagonal rings we produced have sawtooth-shaped edges, giving them metallic characteristics. By adjusting the hydrogen-to-carbon ratio and pressure during growth, we can create a completely new structure unlike conventional graphene.â€
Further tests showed that the microrings formed at the bottom rather than the top of the sheet. Using argon plasma, the top graphene layer could be removed, leaving behind an independent ring. The width of these rings ranges from 10 to 450 nanometers, and this variation affects their electrical behavior. Controlling the width is now the focus of future research.
Tour said, “If we can uniformly produce 10-nanometer-wide graphene ribbons, we can turn them into low-voltage transistors. Such transistors may be ideal for advanced lithium-ion battery storage systems.†(Reporter: Liu Xia)
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