Combinatorial metamaterials

Wednesday 8th September 2010
A seven-nanoshell structure that creates a particular type of interference pattern called a Fano resonance," said study co-author Peter Nordlander, professor of physics and astronomy at Rice. Courtesy:

In 2005, the Engineering and Physical Sciences Research Council UK (EPSRC) awarded the University of Southampton a £6.2m programme grant over six years to establish a Centre for Nanostructured Photonic Metamaterials, manmade media with unusual and useful functionalities that can be achieved by artificial structuring smaller than the length scale of light. Latest news is that Southampton researchers have developed a way to characterise the properties of new photonic metamaterials using combinatorial chemistry.

The ability to make and test thousands of different, structurally related molecules has had a huge impact on the pharmaceutical industry and a company can make (or simulate) thousands of similar molecules in an attempt to identify one in which the required biochemical activity is optimised.

Called combinatorial chemistry the approach is being used by University of Southampton researchers to identify new catalysts, light emitting materials and electronic devices and to discover new metamaterials with unusual electromagnetic properties.

Eric Plum whose February thesis was on 2D and 3D chirality and metamaterials, and a team of researcher set out to create an array of metamaterial samples in which various design parameters vary in a regular way.

They then test each new material with a view to finding one in which the properties are optimised for the kind of photons the team want to manipulate.

They test the idea by creating an array of cells each containing a new metamaterial made of gold square split ring resonators and in which the size of the squares varies from cell to cell in steps of 25nm. They then measured the reflection and transmission properties of each cell and compared the results to computer simulations of their properties.

They are looking for resonance effects that occur at very specific frequencies and which can be fine-tuned by varying factors such as the size of the split rings and the number and thickness of extra layers. These Fano resonances are important as they act like optical switches flicked on by a specific frequency light.

Small but inescapable variations in the manufacturing process inevitably change the resonances, but by comparing simulated and experimental performance, researchers were able to characterise the changes caused by manufacturing variations.

Engineers expect to use Fano resonances in future generations of electronic devices as everything from ultracompact nano antennas to optical memories with a sizeable payoff  for anyone  mastering the technology.

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