Chemists Develop Rules for “Ripping” Graphene

Graphene is one of the most exciting chemical discoveries to come along in the last five years. I’m a synthetic organic chemist, interested in molecules that contain carbon. Because graphene contains only carbons, it’s a target of great synthetic and theoretical interest to organic chemists everywhere. Carbon is a tetravalent compound. This means that one carbon atom can form a total of four bonds to other atoms around it. Normally, organic chemists pull in other elements such as hydrogen, oxygen, and nitrogen in order to fill at least some of these slots. Methane, for example, is a molecule containing one carbon atom with four hydrogens attached to it. Formaldehyde is a carbon with two hydrogens and a doubly-bonded oxygen atom. While some compounds such as benzene can be “carbon rich”, meaning that they contain an abundance of carbon-carbon double bonds, graphene takes this to the extreme. It consists solely of carbon in the form of carbon atoms arranged in a hexagonal grid. Imagine chicken wire, where anyplace two wires touch, there’s a carbon atom. This sheet of fused hexagons makes up the graphene molecule.

Beyond it’s aesthetic qualities, graphene is attracting a lot of attention for it’s material properties and potential usefulness in electronics. The electrons in the carbon-carbon bonds of graphene are not locked down into one position. Because the molecule is flat and all of the hexagons are fused together, some of the electrons are free to shuttle over the surface of the molecule. When they reach the edge of the molecule – the edge – the shape of the rip through the molecular sheet determines the result. If the carbon atoms along the edge of the graphene are in a “zigzag” pattern, the graphene behaves very similarly to a metal. The electrons can flow freely and there is little resistance to their flow. However, if the edge of the graphene sheet is in an “armchair” pattern, the molecule behaves more like a semiconductor; it can let current flow in some instances, and resist the passage of electricity in others. This type of behavior is ideal for producing electronic components such as transistors, and given that graphene is so conductive over it’s bulk, graphene has the potential to replace many of the molecules currently in use for electronic circuits.

Up until now there hasn’t been a good way of predicting how a rip / tear in a sheet of graphene will behave. If the rip produces a zigzag edge it will produce an entirely different electrical behavior than an armchair-shaped rip. Chemists have been searching for rules that will allow them to predict which shape will be produced in a given situation. A recent paper in the American Chemical Society Nano Letters finally gives methods which can be used to predict this behavior. Chemists from California took a look at dozens of examples and then used computer simulations to develop an algorithm. Using this method, it was shown that (with the correct amount of force), the precise rip pattern could be predicted. It was important not to apply too much force, as the graphene sheet is only one atom thick and could be easily torn. However, if just the right amount of pressure was applied, the sheet would rip along predictable and easily identified patterns. The analogy I would use is a piece of perforated paper. It can be ripped in half with enough force, and the tear will be jagged and without any real pattern. However, with just enough force the perforation (a line of weakness) will be followed and the desired shape can be obtained.

This result should help manufacturers produce reproducible batches of graphene with the correct electronic behavior. It’s one step closer to the eventual goal of all-carbon electronics.

The source of this article can be found at:

Kim, K., et al. “Ripping graphene: preferred directions”. Nano Lett. 2011, 12, 293-297.


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