Gardening on the nanoscale

Silicon carbide nanowires could improve solar cell efficiency.

Flowers, trees and grass are all being grown at nano proportions by researchers at the Cambridge Nanoscale Science Laboratory in the UK. But these structures are not just an exercise in aesthetics; they could lead to new water-repellent coatings and solar cells.

The nanoflora are sculptured from miniature wires of silicon carbide a thousand times thinner than a human hair. A gas mixture containing methane is passed across a silicon chip where it reacts with tiny droplets of Gallium on its surface to form silicon carbide. The size and shape of the crystalline structures can be altered by tweaking the temperature and pressure as the wires grow.

A typical flower is composed of an intertwined stem and a bulbous head consisting of a tight bundle of nanowires, each between 100nm and 200nm in diameter. There could be several applications for these intricate structures, says Mark Welland, professor of nanotechnology at the University of Cambridge, UK. These kinds of nanostructures are responsible for water-repellent coatings in nature, he says, causing water to roll off the wings of butterflies and drop from the leaves of lotus flowers.

Preliminary tests suggest that the wire flowers repel water at room temperature and even at 80°C. ’Water droplets roll off these surfaces when they are tilted at angles as small as five degrees,’ says Welland. Coating car windscreens and clothes with these nanoflowers might put an end to windscreen wipers and anoraks, he speculates.

The nanoflowers could also be used to optimise the efficiency of solar cells which comprise conducting polymer mixed with an inorganic nanostructured material. ’With the materials we have developed there is the real possibility of further improving the design of these solar cells by producing the inorganic component with the precise morphological and material properties,’ he says.

Henry Nicholls