Boron may be the next wonder material

For example, if metallic ribbons of boron are stretched, they morph into anti-ferromagnetic semiconducting chains, and when released they fold back into ribbons.

Experimental labs are making progress in synthesising atom-thin and fullerene-type boron, which led Boris Yakobson, researcher at Rice University in the US to think 1-D boron may eventually become real as well. Yakobson’s lab creates atom-level computer simulations of materials that do not necessarily exist yet. Simulating and testing their energetic properties helps guide experimentalists working to create real-world materials.

Carbon-atom chains known as carbyne, boron fullerenes and two-dimensional films called borophene, all predicted by the Rice group, have since been created by labs. “Our work on carbyne and with planar boron got us thinking that a one-dimensional chain of boron atoms is also a possible and intriguing structure,” said Yakobson.

One-dimensional boron forms two well-defined phases -chains and ribbons – which are linked by a “reversible phase transition,” meaning they can turn from one form to the other and back. To demonstrate these interesting chemomechanics, the researchers used a computer to “pull” the ends of a simulated boron ribbon with 64 atoms.

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This forced the atoms to rearrange into a single carbyne-like chain. In the simulation, researchers left a fragment of the ribbon to serve as a seed, and when they released the tension, the atoms from the chain neatly returned to ribbon form.

“Boron is very different from carbon. It prefers to form a double row of atoms, like a truss used in bridge construction. This appears to be the most stable, lowest-energy state,” Yakobson said. “If you pull on it, it starts unfolding; the atoms yield to this monatomic thread. And if you release the force, it folds back,” he said.

“That makes it an interesting combination: When you stretch it halfway, you may have a portion of ribbon and a portion of chain,” he said. “Because one of them is metal and the other is a semiconductor, this becomes a one-dimensional, adjustable Schottky junction,” he added.

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A Schottky junction is a barrier to electrons at a metal-semiconductor junction and is commonly used in diodes that allow current to flow in only one direction.

The study appears in the Journal of the American Chemical Society.