April 23, 2024

There are many forms of carbon. There are many forms of carbon, including graphite and diamond. The thinnest material known is graphene. It has just one atomic layer, which makes it an exciting candidate for future electronics and high-tech engineering applications. Each carbon atom in graphene is linked to three neighbors, creating hexagons arranged in a honeycomb structure. Although theoretical studies have shown that carbon molecules can form flat network patterns while binding to three neighbors, these predicted networks have yet to be realized.

Researchers from the University of Marburg, Germany, and Aalto University, Finland, have discovered a new network of carbon that is atomically thin as graphene but contains squares, hexagons, and octagons, which form an ordered lattice. The unique structure of this network was confirmed by high-resolution scanning probe microscopy. Its electronic properties were also very different from graphene.

The new Biphenylene network, as it is called, has metallic properties. This contrasts with graphene and other carbon forms. The network’s 21-atom broad stripes behave like a metal. Graphene, at this size, is a semiconductor. Professor Michael Gottfried from the University of Marburg is the lead author of the idea. Qitang Fan, a Marburg-based researcher, said the novel carbon network could also be used as an anode material for lithium-ion batteries. It has a higher lithium storage capacity than graphene-based materials.

Aalto University’s team helped to image the material and determine its properties. Professor Peter Liljeroth’s group performed high-resolution microscopy to show the structure, while Professor Adam Foster and his team used computer simulations and analysis for exciting electrical properties.

This new material is created by assembling carbon-containing molecules on a smooth gold surface. The molecules form the first chains, which are composed of linked hexagons. A subsequent reaction then connects the chains to create squares and octagons. The chiral nature of the chains means they can exist in two mirroring types, like right and left hands. Only chains of the same kind can aggregate on the gold surface and form well-ordered assemblies before they connect. This is crucial for forming the new carbon material because the reaction between different types of chains only leads to graphene. Linghao Yan, who conducted the high-resolution microscopy experiment at Aalto University, says that the new idea is to use molecular precursors that have been modified to yield biphenylene.

The teams are working to produce larger sheets of material for further research. Professor Liljeroth said they are “confident” that the new synthesis process will lead to other novel carbon networks.

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