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25 September 2009
An international team of scientists have made the first example of an elusive class of graphene-related materials, predicted more than a decade ago to have exciting electronic properties.
Roman Fasel, at the Swiss Federal Laboratories for Materials Testing and Research, Thun, and colleagues assembled aryl building blocks on a silver surface to form a 2D polymer network with a honeycomb-like structure.
Scanning tunnelling microscopy image of CHP molecules adsorbed on a silver surface
The material is like a porous graphene, describes Fasel, with single atom-wide holes - a trait he predicts will have an interesting effect on its electronic properties. The properties could be chemically tuned by altering the geometric structure or topology of the network, he adds, making them suitable materials for semiconductors or sensors.
Graphene-related materials are widely sought after and have been pursued using top-down lithographic techniques, where the substrates are printed on to a surface. But this approach lacks resolution and precision. Fasel's bottom-up method, which relies on self-assembly, leads to fewer defects in the repeating structure. 'It's natural to use something 2D [the silver surface] to guide the assembly of 2D polymers,' Fasel explains.
'This is an important direction to go in,' comments Dieter Schlüter, an expert in polymer chemistry from the Swiss Federal Institute of Technology, Zürich, Switzerland. But he notes that some defects do persist and currently limit the material's use in electronic devices: 'There are no healing opportunities, which limits the chance for larger ordered systems.'
The defects arise due to the network growing from multiple nucleation sites. Fasel says that a better understanding of the structures' growth mechanisms will help minimise their occurrence.
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Link to journal article
Porous graphenes: two-dimensional polymer synthesis with atomic precision
Marco Bieri, Matthias Treier, Jinming Cai, Kamel Aït-Mansour, Pascal Ruffieux, Oliver Gröning, Pierangelo Gröning, Marcel Kastler, Ralph Rieger, Xinliang Feng, Klaus Müllen and Roman Fasel, Chem. Commun., 2009, 6919
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