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Dr Johan Carlsson, Accelrys Contract Research Scientist

Dr Johan Carlsson, Accelrys Contract Research Scientist

 


The final presentation in our recent contract research webinar series features work on graphene, which has been described recently as the “ultimate” material for next-generation nanoelectronics development. I asked Johan Carlsson from the Accelrys contract research team to provide some background on this nanomaterial. Attend the webinar to see how simulation methods have helped and are helping unravel some of graphene’s secrets.

 

Graphene is one of the most interesting nano-materials at the moment [1,2]. With all the hype, it might seem as though graphene is a completely new material discovered just recently. And in a sense this is correct.

 

When I started to work on carbon materials some eight years ago, graphene was just an imaginary model system. Back then the excitement about the fullerenes was being replaced by what I call the “nanohype.” All the fashionable forms of carbon suddenly needed to have names including the buzzword “nano.” So we had nanohorns, nanofoams, nanoporous carbon, and, of course, nanotubes.

 

These fashion changes indicate the cyclic nature of carbon science. During the last 25 years, a new form of carbon has been discovered every five to six years. The fullerenes were discovered in 1985 [3], the nanotubes in 1991 [4], and, in 1998, graphynes were predicted [5]. That same year, thin graphite layers were grown on top of SiC wafers—what might today be referred to as the first few layers of graphene [6]. However, it took another cycle of carbon science before the graphene hype really took off, when researchers at the University of Manchester managed to extract individual graphene sheets from a graphite crystal in 2004 [7]. It’s actually about time for another carbon allotrope to emerge on the scene. Graphanes (graphene sheets fully saturated by hydrogens) have potential, but they are not strictly pure carbon structures [8]. We’ll have to see if some other new carbon material will emerge soon.

 

Yet while humans have only discovered the potential of graphene recently, graphene sheets have always been available in nature as two-dimensional layers that are the building blocks of graphite. They’ve just not been accessible, as individual graphene sheets have been very difficult to isolate. The barrier to graphene synthesis was perhaps more mental than technical, as the method that finally succeeded was incredibly simple. The reseachers in Manchester had the ingenious idea to use adhesive scotch tape to lift off the graphene sheets from a graphite crystal! [7] Of course, this method didn’t scale industrially, and since this breakthrough a number of alternative methods have been quickly developed.

 

Graphene is now a mature material. Perhaps the maturation of graphene has represented the next step in the cyclic carbon evolution? Anyway, the progress in this field has been rich because graphene science straddles two different communities: the nanotube community and the low dimensional semiconductor community. Graphene has been proposed for a variety of applications in diverse fields, including field effect transistors with graphene channels [9], gas sensors [10], and solar cells [11]. It’s even attracted interest in life science as an active membrane that can separate different molecules out of a solution [12].

 

Interestingly, the progress in graphene science is to a large extent driven by theoretical predictions and results from simulations. Graphene has been the model system of choice for theoretical investigations of sp2-bonded carbon materials. As such it has been the starting point to study graphite, fullerenes and nanotubes. Many properties of graphene were then known from theoretical point of view, before it was possible to perform actual measurements. The electronic structure of graphene for instance is known from theoretical calculations performed more than 60 years ago [13]. Only recently has it been possible to actually measure the bandstructure of individual graphene sheets. Similarly, a substantial amount of our knowledge about the structure and properties of point defects and edges of graphene was first obtained by simulations and later confirmed by experiments. This shows that simulations and experimentation go hand in hand, and theoretical methods will continue to play a major role in the further development of the graphene and other materials.

Literature


[1] A. K. Geim and K.S. Novoselov, Nature Materials 6, 183 (2007).
[2] A. K. Geim,Science 324, 1530 (2009).
[3] H. W. Kroto, J. R. Heath, S. C. O'Brien, R. F. Curl & R. E. Smalley, Nature 318, 162 (1985).
[4] S. Iijima, Nature 354, 56 (1991).
[5] N. Narita, S. Nagai, S. Suzuki, and K. Nakao,  Phys. Rev. B 58, 11009 (1998).
[6] I. Forbeaux, J.-M. Themlin, and J.-M. Debever, Phys. Rev. B 58, 16396 (1998).
[7] K.S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A. A. Firsov, Science 306, 666 (2004).
[8] J. O. Sofo, A. S. Chaudhari, and G. D. Barber, Phys Rev. B 75, 153401 (2007).
[9] Yu-Ming Lin, Keith A. Jenkins, Alberto Valdes-Garcia, Joshua P. Small, Damon B. Farmer and Phaedon Avouris, Nano Lett. 9, 422 (2009).
[10] F. Schedin, A. K. Geim, S. V. Morozov, E. W. Hill, P. Blake, M. I. Katsnelson, and K. S. Novoselov,  Nature Materials 6, 652 (2007).
[11] X. Wang, L. Zhi, and K. Mullen, Nano Lett. 8, 323 (2008).
[12] S. Garaj, W. Hubbard, A. Reina, J. Kong, D. Branton, and J. A.  Golovchenko, Nature 467, 190 (2010).
[13] P. R. Wallace, Phys. Rev. 71, 622 (1947).

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