Borophene competition to graphene

Chemists have produced the first experimental evidence of the existence of borophene – a single-atom sheet of boron. Taking the form of a hexagonal symmetrical disc with a hole in the middle; this new material is predicted to be fully metallic and a better conductor than graphene. Since the discovery of graphene, chemists have pondered the prospect of a single-atom sheet of boron. Theoretical work suggested it was possible and a team from Brown University has determined that a unique arrangement of 36 boron atoms in a flat disc with a hexagonal hole in the middle might be the preferred building block of borophene. Boron has one fewer electron than carbon and so can’t form the honeycomb lattice that graphene can. Instead, theories suggested atoms were arranged in a triangular lattice with hexagonal vacancies. “That was the prediction, but nobody had made anything to show that’s the case,” said Lai-Sheng Wang, professor of chemistry. Wang’s team have now produced the first experimental evidence that such a structure is possible, and have published their results in Nature Communications. “It’s beautiful,” said Wang. “It has exact hexagonal symmetry with the hexagonal hole we were looking for. The hole is of real significance here. It suggests that this theoretical calculation about a boron planar structure might be right.” It might be possible to use B₃₆ as a basis to form an extended planar boron sheet, a sheet of borophene. Researchers zapped chunks of bulk boron with a laser to create a vapour of boron atoms which they froze into tiny cluster of atoms with liquid helium. These atoms were zapped with a second laser to knock an electron out of the cluster – the speed of this electron determines the cluster’s electron binding energy spectrum, a fingerprint of the cluster’s structure. B₃₆ was shown have an extremely low electron binding energy compared to other boron clusters, and suggested a symmetrical structure. Computation modelling investigated more than 3,000 possible structures of the 36 atoms, before settling on the predicted hexagonal structure. Further investigation confirmed the structure. Wang said the boron-boron bond is incredibly strong so borophene should also be very strong. It is predicted to be fully metallic and could be a better conductor than its graphene counterpart. “That is if anyone can make it,” he said. Planar hexagonal B36 as a potential basis for extended single-atom layer boron sheets