Biphenylene Network: A Nonbenzenoid Carbon Allotrope
Q.T. Fan, L.H. Yan, M.W. Tripp, O. Krejči, S. Dimosthenous, S.R. Kachel, M.Y. Chen, A.S. Foster, U. Koert, P. Liljeroth, J.M. Gottfried
Science 372 (2021) 852
Not graphene: Dr. Qitang Fan and coworkers of SFB 1083 discover new type of atomically thin carbon material
Carbon exists in various forms, of which graphene is one of the most astonishing. In this atomically thin material, each carbon atom is linked to three neighbors, forming hexagons arranged in a honeycomb network. Researchers in the SFB 1083 projects A4 (Gottfried) and A8 (Koert/Duerr) have now discovered a new carbon network, which is planar like graphene, but is made up of squares, hexagons, and octagons forming an ordered lattice. In collaboration with physicists from Aalto University in Finland, the unique structure was confirmed using high-resolution scanning probe microscopy methods. In addition, it was found that the electronic properties of the new material are very different from those of graphene.
Biphenylene network, as the new material is named, is made from organic molecules on an atomically smooth gold surface. These molecules first form polymer chains, which consist of linked hexagons. A subsequent reaction connects these chains and forms the squares and octagons. An important feature of the chains is that they are chiral. Chains of the same type aggregate on the gold surface forming well-ordered assemblies, before they connect. This is critical for the formation of the new carbon material, because reaction between two different types of chains leads to the well-known graphene.
In contrast to graphene and other forms of carbon, the new material has metallic properties. Therefore, it can be used as conducting wires in future carbon-based electronic devices. The authors of the study are confident that their synthesis method will contribute to the discovery of further novel carbon networks. For now, their goal is to prepare larger sheets of the material and to study its interface-related properties.