Defects in Graphene ‘honeycomb’ a boon for nanoelectronics
Graphene. The familiar honeycomb picture jumps out of every high-school chemistry book. The atom-thick sheet made up of six-carbon ring hexagonal lattice is touted as a wonder material. It is the building block of graphite. It is touted as a wonder material owing to its purity, tensile strength, conductive, and optical properties. Despite its uniqueness, the uses of graphene in electronics are limited. Why? Graphene lacks a bandgap which is crucial in semiconductors. In semiconductors, electrons can jump from one band to another which requires a minimum amount of energy. This energy difference is called a ‘bandgap’. To make graphene usable in nanoelectronics we need ways to open the bandgap.
Introduction of defects in planar structure of graphenes is one way to influence its physical properties. Tiny alterations in atomic structure have been predicted and in some cases experimentally shown to have energetically stable graphene. Sounds fairly easy but actual chemical synthesis of such topological alternants has proved difficult.
In a recent work published in JACS from Dr Junzhi Liu’s Topological Carbon Nanostructures Laboratory (TCNL) at the University of Hong Kong, scientists have successfully devised an efficient way to synthesize defective nanographene containing 7–5–7-membered carbon rings instead of 6-membered rings. They synthesized three types of compounds. The first adopts a planar structure similar to normal graphene whereas the other two have a saddle-shaped bent geometry.
The group performed several experiments to characterize these compounds. One of them was the superconducting quantum interfering device (SQUID) measurements. Lovely name with an interesting job. SQUID measures extremely subtle magnetic fields in the order of attotesla (10^-18 …..really, really small). These measurements showed that the 7–5–7 compound has closed-shell antiaromaticity. Earlier studies have shown synthesis of 5–7-membered rings with open-shell features. In polycyclic hydrocarbons, an open-shell structure has unpaired or partially unpaired electrons giving rise to stability issues. Close-shells on the other hand renders the nanographene with high air stabilities over a long period of time giving them a superior edge. The more stable a compound remains in the air the easier it gets to study and engineer it. The chemical synthesis strategies put forth by the scientists here can be used to manufacture more stable nanographene with improved electronic properties in the future.
**The paper can be found on Researchgate here.**
