Diamond-like graphene

Materials World magazine
1 Feb 2018

Ellis Davies reports on a new process for creating diamene, a flexible material as hard as diamond.  

A process for creating diamene – flexible, layered sheets of graphene – which temporarily becomes harder than diamond and impenetrable upon impact, could help protect the body and fragile objects. Researchers at the City University of New York (CUNY), USA, also found that the impact causes a sudden reduction in electric current, which suggests that diamene could have electronic and spintronic properties. They tested how two layers of graphene, each one-atom thick, could be transformed into the diamond-like material upon impact at room temperature. 

 Angelo Bongiorno, Associate Professor of Chemistry at the College of Staten Island, CUNY, explained diamene’s uses and properties to Materials World. ‘It could be used as an ultra hard and ultra light protective coating, as its properties are stiffness, comparable to that of diamond, and low-dimensionality. There could be other applications and uses of diamene, we are working on it.’ 

Diamene is a name given to a single layer of diamond, but almost coexists with bilayer graphene – the latter being more stable under standard conditions, the former being easily produced by pressing upon a bilayer graphene film. 

The process started with the growing of the bilayer film of graphene on silicon carbide. The team then used an atomic force microscope tip to press on the film to form a diamond like alternative. This indentation process is carried out at room temperature, with pressures applied ranging between 1–10GPa.

‘Originally, we wanted to indent bilayer graphene with an atomic force microscope tip to measure its transverse stiffness,’ said Bongiorno. ‘The results showed that the stiffness was unexpectedly large and further inspection led to the discovery of diamene. We didn’t develop the production process, it is an indentation process of a particular starting material.’

The team reports, in the paper Ultrahard carbon film from epitaxial two-layer graphene published in Nature Nanotechnology, that density functional theory calculations suggest that, upon compression, the two-layer graphene film transforms into a diamond-like film, producing both elastic deformations and sp2 to sp3 – hybridisation – chemical changes.

Just the beginning

Following the discovery, the team aims to improve and modify the indentation process to stabilise the diamond-like film. ‘We are working in two opposite directions – to understand the fundamental (atomistic) mechanisms that make both diamene, and the hardening effect that stems from its formation, possible,’ said Bongiorno. ‘Furthermore, we are working to enhance spatial resolution and to implement techniques to stabilise the diamond film after its formation.’

The team does not yet know if the process is scalable to a commercial level, as more research is required. ‘The material and production process look promising, and there are still important basic and technical questions that we need to address,’ added Bongiorno. ‘In short, the scalability question is too far down the road from where we stand right now.’ 

Working on the underlying mechanisms present in the formation of diamene, and the hardening effect, could lead to further discoveries. Researchers think that that there might be some generality in the observed phenomena – other 2D materials might behave the same as bilayer graphene, when supported by the right substrate. In brief, said Bongiorno, ‘diamene could be the first of a list of new 2D materials’’