New form of "Mobius" carbon predicted

In 1858, August Mobius dreamt up a shape with a single surface and only one edge. The Mobius strip has fascinated children and scientists alike since then.

How small can these shapes be? In December 2003, German chemists made a molecular Mobius strip out of a benzene-like ring modified with a belt-like carbon structure. Since then, various groups have produced increasingly bizarre Mobius-type molecules, including one that can switch back and forth from a Mobius to an ordinary strip when zapped with light.

Of course, the obvious choice of material with which to make Mobius molecules is graphene. But this particular trick has eluded chemists, an omission that clearly irks. Now Douglas Galvao from the Universidade Estadual de Campinas in Sao Paolo, Brazil, and buddies have decided to grip the bull by the horns and calculated the properties that Mobius carbon might have.

Their technique is to simulate the way carbon atoms behave when joined together to firm a band of graphene. They then added a half twist to the simulated band and repeated the calculation, and so on for additional half-twists (obviously, only those with an odd number of half twists produce a true Mobius strip with one edge and one surface).

Galvao and co make a number of predictions about the shapes and properties such strips might have, such as that they are stable at temperatures of at least 500 Kelvin. But the most interesting is this: they say that strips with an odd number of half twists (and one with six half turns, for some strange reason) ought to have a magnetic dipole moment. And that should make the molecules crystalise.

So what Galvao and co are predicting is a new form of crystalline carbon made entirely of Mobius-molecules of graphene.

How likely are we to see such a substance? There are no guarantees but the rate at which chemists are falling over themselves to outdo each other with graphene means that Mobius carbon could be with us sooner rather than later.

Ref: arxiv.org/abs/0903.2080: Mobius and Twisted Graphene Nanoribbons: Stability, Geometry and Electronic Properties.