The increasing importance of crystalline nanomaterials in nanotechnology has sparked much research towards controlling their structures and morphologies — which in turn determine their properties. Chromium silicide, a narrow-bandgap semiconductor with high melting point and resistance to oxidation, has attracted interest in a wide range of areas, including electronics and energy materials. Now, Tom Wu and co-workers from Nanyang Technological University in Singapore have prepared a chromium silicide single crystal that adopts an unusual hexagonal structure resembling a spider-web (pictured; J. Am. Chem. Soc. 132, 15875–15877; 2010).

Chromium silicide crystalline nanowires can be prepared by a vapour diffusion method under a flow of argon. By suddenly increasing the gas flow and adjusting vapour concentrations of the components during the crystallization, Wu and co-workers induced a change of direction in the nanowire growth, giving rise to two-dimensional hexagonal structures (nanowebs). These grew to be around 150–200 nm in diameter and 10–30 nm thick and were found to be highly crystalline, even at the corners between each nanowire segment.

Credit: © 2010 ACS

Opposite sides of the nanowire segments are oppositely charged, which the researchers suggest is what induces the nanowebs' formation. This would also mean that the walls of the nanowires form charged planes perpendicular to that of the nanoweb, which is in good agreement with the structures observed, and is supported by calculations of the electrostatic energies for different bending possibilities. At most corners, depending on the distance between the walls, the nanowires either grow into a continuous nanoweb or reverse their direction — linear or zig-zag nanowires are only rarely observed.

The original version of this story first appeared on the Research Highlights section of the Nature Chemistry website.