Graphene: from a conceptual material to a material of the future

Costas Galiotis
FORTH/ ICE-HT and Dept. Materials Science, University of Patras

Graphene is a perfect 2D crystal of covalently bonded carbon atoms and forms the basis of all graphitic structures[1,2].

The material was well known as a concept structure (platform) to mathematicians and modellers for many years and to the material physicists and scientists as an individual layer of crystalline graphite.

However, its isolation and characterisation by Geim and Novoselov in 2005[3] has given rise to a dramatic surge in research and potential applications for this material.

Graphene is the best conductor of heat we know, the thinnest material, it conducts electricity much better than silicon, is 100-300 times stronger than steel, has unique optical properties, it is impermeable already as a monolayer, just to mention a few of its characteristics.

Either separately or in combinations, these extreme properties can be exploited in many areas of research; new possibilities are being recognised all the time as the science of graphene and other two-dimensional materials progresses.

Secondly, graphene science and technology relies on carbon one of the most abundant materials on Earth. It is an inherently sustainable and economical technology.

Thirdly, graphene is a planar material and as such compatible with the established production technologies in information and communication technologies.
Regarding mechanical properties which are being examined by our group, graphene is considered one of the stiffest and strongest material in nature combined with high inherent ductility.

In spite of that, very little experimental verification has been provided for its extraordinary mechanical properties. Strain on the other hand has been shown to modulate graphene’s electronic, magnetic and transport properties.

Hence is of outmost importance to understand how the thinnest membrane ever existed in nature can respond to mechanical load.

In general it is expected and already verified experimentally by us and others, that a thin film can withstand relatively large tensile strains in air without early fracture, whereas in compression monolayer graphene is expected to buckle at extremely low strains.

Direct evidence of buckling by means of AFM measurements has already been shown.

Yet axial tensile fracture at the expected strains of over 30% has never been seen or attained.

In fact, the only indication of the high tensile strength and ductility of graphene stems from a number of modelling simulations in which the flake geometry has been largely ignored.

Furthermore, for typical rectangular graphene flakes it is self-evident that when the flake is stretched axially in one direction, Poisson’s contraction in the other direction will immediately induce (lateral) buckling.

This very interesting phenomenon which should be prevalent for any future 2D materials, has not as yet been fully studied, predicted or, even, exploited.

Furthermore, our results show that graphenes embedded in plastic beams exhibit remarkable compression bucking strain compared to that of the suspended ones, due to the effect of the lateral support provided by the polymer matrix, which is indeed dramatic and increases the effective flexural rigidity of graphene by 6 orders of magnitude.

The experimental finding that one atom thick monolayers embedded in polymers can provide reinforcement in compression to high values of strain is very significant for the development of nanocomposites for structural applications[4].

Interface interactions that lead to tensile and/or compression stress transfer from a polymer matrix to a graphene flake is also of extreme interest particularly for composite applications.

Finally, recent attempts to take off graphene research in Greece will be covered. The creation of the FORTH Graphene Centre will be discussed and the possibilities of collaborative work with other institutions and groups will be explored.

References
[1] Q.Z. Zhao, M. B. Nardelli, J. Bernholc, Phys. Rev. B , 65 (2002) 144105
[2] C. Lee, X. D. Wei, J. W. Kysar, J. Hone, Science, 321 (2008) 385
[3] A. K. Geim , K. S. Novoselov , Nat. Mater., 6 (2007)183
[4] O. Frank, G. Tsoukleri, J. Parthenios, K. Papagelis,

Read more: www.demokritos.gr

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