Gold blends

A pioneering molecular-manufacturing process is creating a new generation of materials for use in industries as diverse as pollution detection and magnetic memory storage.

The process creates a ‘metamaterial’ of gold by engineering cavities on a nanoscale within the gold. Metamaterials are engineered composites with completely different chemical properties to their constituent materials. Researchers at the University of Southampton have already developed a greenhouse gas sensor from the metamaterial and are working on developments in optical communication and magnetic memory.

To produce the metamaterial the researchers first mix particles of soap with water. On a molecular level soap consists of tiny ‘rods’, one end of which is attracted to water, the other repelled by water.

This reaction can be controlled to form an intricate network of soap particles that researchers use as a template.

In the second part of the process the soap is covered in gold, then the soap is washed away, leaving a metamaterial with a honeycomb structure.

When greenhouse gases pass through this honeycomb structure, they react with air in the cavities and the gold heats up. Thistemperature change provides an ideal sensor for greenhouse gas detection.

The honeycomb holes in the metamaterial can themselves be used to create other applications. For example, magnetic particles can be arranged inside the cavities and used for magnetic storage of data.By changing the size of the cavities, researchers discovered that air inside the cavities reacts with the gold to created red and blue gold.

The colouration could eventually be used as a switch between different colours of light in optical fibres. This would allow information stored in different wavelengths of light to be transmitted more quickly through optical networks.

Leading the research, Jeremy Baumberg, professor of physics and astronomy at Southampton, claims his research is a departure from others working in the field. ‘Other researchers are creating nano-particles that are hard to control and can escape anywhere. They are looking at what these particles do when they bond with other molecules,’ he said.

‘We are creating metamaterials using a film of gold. The advantage over other nanotechnology developments is that our films stay exactly where you want to put them.’

Baumberg’s team is also using the process to create meta-materials from plastics and semiconductors.

The greenhouse gas detector is being manufactured by Southampton spin-out City Technology.