"The process is rapid and can be run continuously – all we do is inject methanol into the growth vessel and collect the nanowires in solution, which means that they can be readily processed for device integration," Simon Henley of Surrey's Advanced Technology Institute told nanotechweb.org. "We estimate that we could produce gram quantities per hour, but this figure could be increased with a more powerful laser and by firing the laser more rapidly."

Iron oxide nanostructures have a wide range of possible applications, including lithium ion battery electrodes, gas sensors and field-effect transistors. In addition, iron oxide's magnetic phases are of considerable interest for developers of high-density information storage media.

Shaping up
To make its material, the group uses an ultraviolet (248 nm) pulsed-laser ablation technique (pulse duration = 25 ns, repetition rate = 25 Hz). Emission from an excimer laser is raster scanned over the bottom of a vessel containing iron oxide power and methanol.

The high temperatures and pressures induced at the laser's focal spot cause the surrounding solvent to boil. This process violently ejects iron particles away from the bottom of the vessel and back into the path of the laser beam, which can be observed as bright flashes of light.

Henley and his colleagues believe that a photochemical or photothermally assisted reaction between methanol and the ablation products is responsible for the growth of nanobelts in solution. They go on to explain that subsequent interaction between the laser and the nanobelt-shaped material initiates a fragmentation process that breaks up the primary product into nanowires.

This means that the residence time of the products within the growth vessel is key to controlling the morphology of the iron oxide nanostructures. High collection rates yield nanobelts and low collection rates yield nanowires.

Back in the lab, the team is now busy investigating the electrical properties of its nanostructures with a view to producing nanoscale electronic devices, such as field-effect transistors.

The researchers presented their work in Nanotechnology.