Credit: © 2008 AAAS

Molecules routinely self-assemble into close-packed arrays and periodic structures. The scientific and device-specific relevance of such ordered networks is clear. However, networks with weaker order are important to systems such as quasi-crystals, glasses and antiferromagnetics.

Now, Peter Beton and colleauges1 at the University of Nottingham have succeeded in creating a near-ideal, random tiling of a graphite surface with the organic molecule TPTC. Two TPTC molecules can bond to each other in two different configurations: parallel, and 'arrowhead', which introduces randomness into the resulting network. Furthermore, the geometry of TPTC bonding is unique: if each molecule in the network is inscribed into a rhombus, the intermolecular bonds fall on the rhombus edges. This mathematical correspondence causes the TPTC network to have hexagonal orientational order (all voids fall on a hexagonal lattice), without translational symmetry (translation will not necessarily give the same atomic arrangement).

The structure of the network also allows Beton and co-workers to do some interesting things. They observe a triangular void defect moving through the molecular network, and are able to determine the energetics of the two bonding configurations from the network's spatial correlations. They also suggest that such systems may be useful analogues for other materials, such as glasses.