With their unique mechanical and electronic properties, carbon nanotubes are appealing building blocks for the construction of nanoscale devices. Now, in an Olympic feat of nanoengineering, Chad Mirkin, George Schatz and co-workers from Northwestern University in the USA have demonstrated how carbon nanotubes can be bent into circular structures, as shown in this image, using a patterned surface as a template (Nano Lett. doi: 10.1021/nl062258e; 2007). Bending nanotubes is of particular interest because it allows their unusual curvature-dependent properties to be studied.

Dip-pen nanolithography was used to coat a gold surface with a monolayer comprising circular islands of hydrophilic molecules surrounded by a sea of hydrophobic ones. When the nanotubes were placed on this surface, they assembled along the boundaries between the hydrophobic and hydrophilic regions, forming circles with diameters as small as 100 nm (although the rings in this image are several micrometres across). The formation process is controlled by two opposing forces — the strain energy involved in bending a nanotube and the van der Waals forces between the nanotube and the molecules on the surface. Although nanotube rings have been made previously, this approach can be used to pattern circles of defined diameters on a surface.