Beyond Graphene: Graphyne and Graphane
By Will Soutter
Graphene was discovered at the University of Manchester in 2004, and is a one atom thick substance with incredible electronic and mechanical properties. Graphene has taken the world of nanoscience research by storm, and a huge number of potential applications for the material have been proposed.
Now however, researchers are paying more and more attention to graphene derived materials which may be just as important. Graphane and graphyne differ in chemical structure from graphene, which may give them interesting mechanical or electrical properties which give them an edge over graphene itself in certain applications.
Graphene, as a 2D sheet of carbon atoms, is already viewed as the most basic of the dimensionally limited, carbon-based nanomaterials we know about. A carbon nanotube can be considered as a graphene sheet rolled into a 1D tube, and rolling the sheet up in two dimensions creates a "zero-dimensional" spherical fullerene.
Discovery of this set of carbon nanomaterials has already led to a huge number of practical and theoretical discoveries, so it is understandable that materials scientists are keen to explore the variations in properties and the potential applications of further graphene derivatives.
Graphene is a single sheet of carbon atoms, lined together in a hexagonal pattern.
Graphene's atomic structure consists soley of carbon atoms, each bound to three others,creating a hexagonal pattern. This unusual 2D structure means that graphene’s electronic energy levels pile up into shapes referred to as Dirac cones. These cones permit electrons to travel with energy directly corresponding to their momentum - in other words resistance experienced by the electrons is extremely low, allowing currents to flow easily.
Because these unique electronic properties are highly dependant on the physical structure of the material, they can be modified quite drastically by adding chemical dopants to the graphene, or even by placing it on different substrates.
Graphene’s unique electronic properties allow usage of this material for developing transistors that are very fast and very small. Complex graphene structures like nanoribbons are used for developing these transistors, as the electronic band-gap needed to use graphene as a semiconductor must be created physically.
Graphene has applications is countless other areas too, from the transparent sensor layer in touch screens, to solar cells, batteries and ultracapacitors.
Graphane was developed at the University of Manchester in 2009 by exposing pristine graphene to atomic hydrogen. This causes a chemical reaction in which a single atom of hydrogen is attached to each atom or carbon in the graphene, without causing any damage or change to the 2D hexagonal structure of the material.
Graphane maintains the hexagonal structure of graphene, but with a hydrogen atom attached to each atom of carbon. This video shows an "island" of graphane in the middle of a graphene sheet. Read more about graphane on AZoNano.
Unlike graphene, graphane is an electrical insulator. This could possibly mean that semiconducting patterns on graphene could be made by "painting" the non-conducting parts with hydrogen to create graphane, rather than cutting up the graphene sheet to create nanoribbons and quantum dots. This much simpler fabrication process could lead to faster adoption of graphene transistors in electronic devices.
Simulations have also shown that p-doped graphane will be a high-temperature superconductor, with a TC over 90K. If proved to be true, this would be a momentous discovery - particularly as the superconducting effect would conform to BCS theory, making graphane by far the highest temperature BCS superconductor.
New computer simulations determine that a much advanced version of electronic properties can be found in another sister-material of graphene called graphyne. These computer simulations highlight that the conduction electrons of graphyne travel as fast as graphene, but are limited to travel in just one direction. This will help with designing faster transistors and a variety of electronic components which process one-way current.
Graphyne is structurally similar to graphene, but contains double and triple bonds between carbon atoms. Graphyne’s atoms do not possess a completely hexagonal arrangement - hexagonal units are broken up by other geometries, which leads to the directionality of the material's electrical conductivity. Theoretically, there are a large number of different graphynes with double and triple bonds in arrangements that are slightly different.
Graphyne's properties could make it much more directly applicable to electronics than graphene. However, these properties are the results of simulated calculations, so proof of graphyne's effectiveness will have to wait until it can be synthesized experimentally.
Graphene is one of the most discussed topics in material science and physics, and has numerous futuristic applications in photonics and electronics. Researchers around the world are still working to explore all applications possible for this material.
Graphyne and graphane, on the other hand, have efficient electronic properties, which may make them better suited for applications in transistors and electronic devices than graphene itself. Further research on these new materials will help establish the significance and applications of these materials in a much more in-depth manner.
- Pioneering scientists discover new material - University of Manchester
- Beyond the Wonder Material - Dr Kostya Novoselov, PhysicsWorld
- Doped graphane should superconduct at 90K - Technology Review
- Graphyne Could Be Better Than Graphene - ScienceNOW