Photonic Revolution
Optical technology has given us lasers, fibre optic cables, DVD and Blu-ray, the Internet, to name but a few. The scientists at the University of Southampton’s Photonic Metamaterials Programme, believe the next photonic revolution will be nanotechnological. They have found a way to manipulate light at microscopic levels on the surface of gold to change its colour appearance. This is the first time the visible colour of metal has been changed in this way and could be used in jewellery-making, or as a financial security feature.

To understand the minute scale of a nanometre, consider that a single gold atom is about a third of a nanometre in diameter. Metamaterials are manmade with unusual functionality, which is achieved by artificially manipulating its structures at the nanometre scale and each individual structure is smaller than the wavelength of the incidental light. The nano-patterned metal is therefore a ‘metamaterial’, engineered to provide optical properties not found in nature.

Sandblasting at a nanoscale
Dr Kevin MacDonald is the Research Manager for Southampton's Photonic Metamaterials programme, directed by Professor Zheludev, and also the project leader. He explains how changing the visible colour of metals is just one example of what can be done through nano-patterning and vividly illustrates the power of the paradigm for controlling and manipulating light on the nanoscale.

By embossing tiny raised or indented patterns on the metal's surface, which alters the way it absorbs or reflects light they were able to spell out ‘Nano Meta’ on gold. It’s akin to sandblasting the metal at an atomic level. Their technique means gold can be made red or green or a multitude of other hues and can also be applied to other metals such as silver and aluminium.

Anti-Counterfeiting
They see a number of potential applications for the concept such as, anti-counterfeiting features for banknotes, documents, where unique features could be created that are very difficult to mimic by any means and essentially impossible to truly replicate without access to very high-end fabrication technology. In jewellery design it could used to add colourful decorative features to the metal, such as numerals on a metal clock face in a different hue.

The team is busy patenting their work and negotiating how to move the technology from the research laboratory to commercial production.