The current interest in materials with a 2D honeycomb geometry is due to their unique optoelectronic properties. We realized semiconductors with this geometry by oriented attachment of colloidal nanocrystals; the resulting superstructures are atomically coherent over hundreds of nanometers and have a superimposed nanoperiodicity. [1,3] Kalesaki et al. performed tight-binding calculations which predict that these materials have the conventional band gap of a semiconductor, however with Dirac cones for the conduction electrons and valence holes. 
A remaining question is how hundreds of nanocrystals can form highly ordered superstructures through a non-reversible process like oriented attachment. With in situ GISAXS/WAXS measurements, temporal evolution TEM experiments and Monte Carlo simulations we observed 2D phases with unusual nanocrystal and long-range atomic ordering, yet with the nanocrystals unbound. We propose that such phases are the intermediate phases before covalent facet-to-facet binding occurs.
1. W.H. Evers et al; Low-dimensional semiconductor superlattices formed by geometric control over nanocrystal attachment. Nano Lett. 13, 2317-323 (2013). doi:10.1021/nl303322k
2. E. Kalesaki et al; Dirac Cones, Topological Edge States, and Nontrivial Flat Bands in Two-Dimensional Semiconductors with a Honeycomb Nanogeometry. Phys. Rev. X 4, 011010 (2014). doi:10.1103/PhysRevX.4.011010
3. M.P. Boneschanscher et al; Long-range orientation and atomic attachment of nanocrystals in 2D honeycomb superlattices. Science, Accepted (2014). doi:10.1126/science.1252642