Scientists Synthesize New Allotrope of Carbon

A team of researchers from the University of Marburg and Aalto University has synthesized an ultraflat biphenylene network, which is atomically thin like graphene, but is made up of four-, six-, and eight-membered rings of carbon atoms; while graphene is a semiconductor at this size, scanning tunneling spectroscopy revealed that the new allotrope is metallic.

Biphenylene network: the upper part of the image shows schematically the linking of the carbon atoms, forming squares, hexagons, and octagons; the lower part is an image of the network obtained with high-resolution microscopy. Image credit: University of Marburg / Aalto University.

“These stripes could be used as conducting wires in future carbon-based electronic devices,” said Professor J. Michael Gottfried, a researcher in the Department of Chemistry at the University of Marburg.

“This novel carbon network may also serve as a superior anode material in lithium-ion batteries, with a larger lithium storage capacity compared to that of the current graphene-based materials,” added Dr. Qitang Fan, also from the Department of Chemistry at the University of Marburg.

The researchers obtained planar carbon sheets with four-, six- and eight-membered rings via a synthesis on a gold surface.

Using the high-resolution microscopy and computer simulations, they studied the structure of the material and its electrical properties.

“The new material is made by assembling carbon-containing molecules on an extremely smooth gold surface,” they explained.

“These molecules first form chains, which consist of linked hexagons, and a subsequent reaction connects these chains together to form the squares and octagons.”

“An important feature of the chains is that they are chiral, which means that they exist in two mirroring types, like left and right hands.”

“Only chains of the same type aggregate on the gold surface, forming well-ordered assemblies, before they connect.”

“The new idea is to use molecular precursors that are tweaked to yield biphenylene instead of graphene,” said Dr. Linghao Yan, a researcher in the Department of Applied Physics at Aalto University.

“We are confident that this new synthesis method will lead to the discovery of other novel carbon networks,” added Professor Peter Liljeroth, also from the Department of Applied Physics at Aalto University.

The team’s work is described in a paper in the journal Science.

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Qitang Fan et al. 2021. Biphenylene network: A nonbenzenoid carbon allotrope. Science 372 (6544): 852-856; doi: 10.1126/science.abg4509