While graphene is the wonder material that perhaps usurped the fullerenes and even the nanotubes from the pinnacle of technological interest, there is a new pretender vying for the crown – carbyne.
Carbynes are carbon chains held together by repeating double bonds or alternating single and triple bonds. They are true one-dimensional material lacking the 2D sheet-like nature of graphene and the 3D structure of hollow carbon nanotubes. Now, Boris Yakobson and his group at Rice University, Texas, USA, have calculated that hypothetical carbyne nanorods could be twice as strong as graphene weight for weight [Yakobson, et al., ACS Nano (2013), doi:10.1021/nn404177r].
The team's first-principles calculations also suggest that stretching carbyne as little as 10 percent alters its electronic band gap significantly. A 90-degree end-to-end rotation, they predict, makes it a magnetic semiconductor. Moreover, adding side chains can allow this twist to be controlled as well as allowing materials scientists to get a grip on the chains, appropriate end groups can “switch on” stiffness too or endow it with the capacity to store energy. The team also suggests that carbyne will be stable at room temperature and resist the formation of cross links.
“You could look at it as an ultimately thin graphene ribbon, reduced to just one atom, or an ultimately thin nanotube,” Yakobson explains. “It could be useful for nanomechanical systems, in spintronic devices, as sensors, as strong and light materials for mechanical applications or for energy storage, but regardless of the applications academically, it's very exciting to know the strongest possible assembly of atoms.”
Carbyne is not a new concept, scientists in the 19th century posited its existence and a very similar material was synthesized in the USSR in 1960. It has also been observed in compressed graphite and hypothesized in cosmic dust. The calculations point to carbyne being the highest energy state for stable carbon in contrast to graphite, diamonds, nanotubes and fullerenes which represent carbon's stable “ground states”, the lowest possible energy configurations.
“I have always been interested in the stability of ultimately thin wires of anything and how thin a rod you could make from a given chemical,” Yakobson says. “We had a paper 10 years ago about silicon in which we explored what happens to silicon nanowire as it gets thinner. To me, this was just a part of the same question.”
There are some quite intriguing details in carbyne electronics to be explored, “Yakobson told Materials Today,” like the metal-insulator transition. He adds that exploring whether or not this material could be stabilized within carbon or boron nitride nanotubes is of interest as there have already been experimental hints of that.