For the first time, American scientists have successfully synthesized graphene nanoribbons atom by atom 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 holds great promise for use in next-generation lithium-ion batteries and advanced electronic devices.
James Tour, a physicist at Rice University and one of the lead researchers, explained that traditional methods of growing graphene via chemical vapor deposition typically begin with a small seed or bump on a metal surface like copper. During the nucleation process, carbon atoms attach to the seed, and as more atoms join, they form a mesh-like structure.
To better understand how the first graphene ring forms under high pressure and in a hydrogen-rich environment, the team conducted a series of experiments. They discovered that when graphene grows rapidly, it becomes hydrogenated, and its edge turns into a nucleation site. This allows carbon atoms to be incorporated beneath the existing layer, initiating the formation of a new sheet. However, because the top layer grows quickly, it blocks the flow of carbon atoms to the lower layers, halting their growth and resulting in a single-layer graphene ring. This cycle repeats, building up multiple layers, similar to an onion.
Tour explained, “This mechanism depends on the topmost graphene layer blocking the supply of carbon atoms to the bottom. What we end up with is a multilayered, single-crystal graphene ‘onion ring’.â€
He added, “Typically, if you cut a large piece of graphene, you get nanobelts. But if we can grow them from scratch, we can control the edges, which are crucial for determining the material’s electrical properties. The edges of our hexagonal ‘onion rings’ are all sawtooth-shaped, giving them metallic characteristics. By adjusting the balance between hydrogen and carbon in the growth environment, we can create a completely new structure—very different from regular graphene.â€
Further testing revealed that the microrings formed at the bottom of the sheet, not the top. Using argon plasma, the top graphene layer could be removed, leaving behind a standalone 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 team's next challenge.
Tour said, “If we can uniformly produce 10-nanometer-wide graphene ribbons, we can turn them into low-voltage transistors. These transistors may be ideal for advanced lithium-ion battery applications.â€
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