One-atom-thick gauze considered not possible now really fabricated
Researchers at the University of Nijmegen, the Max-Planck Institute in Stuttgart and the University of Manchester have succeeded in fabricating a layer of graphene in a free-hanging state. Graphene is a new kind of carbon - only one atom thick - and was discovered in 2004. So far, this was only fabricated lying and supported by a substrate of another material. Many textbooks claim that a layer just one atom thick cannot exist in a free state. The researchers have now taken the edge off this statement and, moreover, they have been able to explain the reason why such a thin layer actually is stable. They have this scientific breakthrough published in Nature on March 1, 2007.
In 2004 researchers at the University of Manchester discovered that it is possible to isolate a layer that is only one atom thick from some other crystal layers. An example is graphene, which is the thinnest layer of carbon possible, only one atom thick. It has astonishing properties, which makes it most suitable for an inquiry into all kinds of quantum physical phenomena. So, worldwide, it has become 'hot' material. One top-class publication is succeding another. Thus, on February 15, Science published pieces of news from universities at Nijmegen and The United States of America that the quantum Hall-effect in graphene can also be measured at room temperature. However, so far it was a 'small pencil line' at a substrate. But for the first time researchers have been succeeded in creating the thinnest crystal in a free-hanging state.
Graphene is being made by peeling off a carbon crystal on a sheet of silicon until only one atom layer is left. An important question is whether the then remaining chicken wire-like crystal is able to exist also without substrate. It was anticipated that too much tension would arise within the layer in order to preserve it. That is why most textbooks state that it is not possible to have a free-hanging layer that is only one atom thick. But it is possible now.
Experimental physicists led by Dr. Jannik Meyer (Max-Planck-Institut für Festkörperforschung in Stuttgart) and professor Andre Geim (University of Manchester), together with theoretical scientist professor Mikhail Katsnelson of the Institute for Molecules and Materials at Radboud University Nijmegen, are using a technique that is also being used in microchip fabrication. The team has placed a golden scaffold on top of a graphene crystal on a silicon substrate. Then, the substrate was dissolved by using acids. The graphene remained hanging freely on the gold.
Graphene membrane is the thinnest material possible and remains remarkably well preserved. The researchers also accounted for the stability of the thinnest layer: it is not completely flat, but it undulates lightly. This provides for a stable distribution of the powers that occur. Actually, the theory predicts that one-atom-thick layers - the physicists call them two-dimensional crystals - will never be flat, but that they will curve spontaneously and therefore, will look folded. The researchers have now confirmed this by experiment.
The researchers think that in the distant future these membranes may be used as a gas sieve or in ultra-fast electromechanical switches. In the near future, graphene has to be made suitable for invisible support in order to look into complex, bioactive molecules under an electron microscope. "We are now showing that this is basically possible", Geim says. "We are now able to make real things by using existing technology. It is a challenge to manufacture such an atomic gauze cheap and at a large scale".
For more information, please contact Professor Mikhail Katsnelson, Institute for Molecules and Materials, phone +31 (0)24 365 29 95;
Professor Jan Kees Maan, Institute for Molecules and Materials, phone +31 (0)24 365 34 22,
or Science editorial office Radboud University Nijmegen, phone +31 (0)24 361 60 00.
The article is entitled 'The structure of suspended graphene sheets'; the authors are Jannik Meyer1, Andre Geim2, Mikhail Katsnelson3, Kostya Novoselov2, Tim Booth2 and Siegmar Roth1. The article will be published in the scientific journal Nature, on March 1, 2007.
1 MPI (Max-Planck-Institut), Stuttgart
2 Manchester Centre for Mesoscience and Nanotechnology, University of Manchester
3 Institute for Molecules and Materials, Radboud University Nijmegen. Katsnelson is financially supported by FOM (Foundation for Fundamental Research on Matter)