Strongest Material Ever: Carbon's New Champion

Photo: Carbon

Nanoropes or nanorods of carbyne, a chain of carbon atoms, would be stronger than graphene or even diamond if they can be manufactured; © Vasilii Artyukhov/Rice University

Carbyne will be the strongest of a new class of microscopic materials if and when anyone can make it in bulk.

If they do, they'll find carbyne nanorods or nanoropes have a host of remarkable and useful properties, as described in a new paper by Rice University theoretical physicist Boris Yakobson and his group.

Carbyne is a chain of carbon atoms held together by either double or alternating single and triple atomic bonds. That makes it a true one-dimensional material, unlike atom-thin sheets of graphene that have a top and a bottom or hollow nanotubes that have an inside and outside.

According to the portrait drawn from calculations by Yakobson and his group:

• Carbyne's tensile strength – the ability to withstand stretching – surpasses "that of any other known material" and is double that of graphene. (Scientists had already calculated it would take an elephant on a pencil to break through a sheet of graphene.)

• It has twice the tensile stiffness of graphene and carbon nanotubes and nearly three times that of diamond.

• Stretching carbyne as little as 10 percent alters its electronic band gap significantly.

• If outfitted with molecular handles at the ends, it can also be twisted to alter its band gap. With a 90-degree end-to-end rotation, it becomes a magnetic semiconductor.

• Carbyne chains can take on side molecules that may make the chains suitable for energy storage.

• The material is stable at room temperature, largely resisting crosslinks with nearby chains.

"You could look at it as an ultimately thin graphene ribbon, reduced to just one atom, or an ultimately thin nanotube," Yakobson said. It could be useful for nanomechanical systems, in spintronic devices, as sensors, as strong and light materials for mechanical applications or for energy storage. "Regardless of the applications," he said, "academically, it's very exciting to know the strongest possible assembly of atoms."

Based on the calculations, he said carbyne might be the highest energy state for stable carbon. "People usually look for what is called the 'ground state,' the lowest possible energy configuration for atoms," Yakobson said. "For carbon, that would be graphite, followed by diamond, then nanotubes, then fullerenes. But nobody asks about the highest energy configuration. We think this may be it, a stable structure at the highest energy possible."

Yakobson said the researchers were surprised to find that the band gap in carbyne was so sensitive to twisting. "It will be useful as a sensor for torsion or magnetic fields, if you can find a way to attach it to something that will make it twist," he said. "We didn't look for this, specifically; it came up as a side product."

The literature seemed to indicate carbyne "was not stable and would form graphite or soot," he said. Instead, the researchers found carbon atoms on separate strings might overcome the barrier in one spot, but the rods' stiffness would prevent them from coming together in a second location, at least at room temperature. "They would look like butterfly wings," Artyukhov said. "Bundles might stick to each other, but they wouldn't collapse completely," Yakobson added. "That could make for a highly porous, random net that may be good for adsorption." Artyukhov said the nominal specific area of carbyne is about five times that of graphene.; Source: Rice University