Boron has one fewer electron than carbon and as a result can't form the honeycomb lattice that makes up graphene. For boron to form a single-atom layer, theorists suggested that the atoms must be arranged in a triangular lattice with hexagonal vacancies -- holes -- in the lattice.
"That was the prediction," said
Wang and his research group, which has studied boron chemistry for many years, have now produced the first experimental evidence that such a structure is possible. In a paper published on
"It's beautiful," Wang said. "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 may be possible, Wang said, to use B36 basis to form an extended planar boron sheet. In other words, B36 may well be the embryo of a new nanomaterial that Wang and his team have dubbed "borophene."
"We still only have one unit," Wang said. "We haven't made borophene yet, but this work suggests that this structure is more than just a calculation."
The work required a combination of laboratory experiments and computational modeling. In the lab, Wang and his student,
Wang's experiments showed that the B36 cluster was something special. It had an extremely low electron binding energy compared to other boron clusters. The shape of the cluster's binding spectrum also suggested that it was a symmetrical structure.
To find out exactly what that structure might look like, Wang turned to
"As soon as I saw that hexagonal hole," Wang said, "I told Zach, 'We have to investigate that.'"
To ensure that they have truly found the most stable arrangement of the 36 boron atoms, they enlisted the help of
That structure also fits the theoretical requirements for making borophene, which is an extremely interesting prospect, Wang said. The boron-boron bond is very strong, nearly as strong as the carbon-carbon bond. So borophene should be very strong. Its electrical properties may be even more interesting. Borophene is predicted to be fully metallic, whereas graphene is a semi-metal. That means borophene might end up being a better conductor than graphene.
"That is," Wang cautions, "if anyone can make it."
In light of this work, that prospect seems much more likely.
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