Researchers in the Department of Physics and Centre for Plastic Electronics at Imperial have developed a new type of ‘metamaterial’ which uses changes in a molecule’s geometry to change the frequency and direction of the light it emits. The molecules were effectively drawn onto a substrate using a method called ‘dip-pen nanolithography’ and could change the way scientists design and develop optical materials for technological use.
This new feat of metamaterial engineering, described in Nature Communications, allows researchers to deposit certain types of organic polymer (long chains of repeating molecular units) on a substrate using the ‘dip-pen’ technique. This causes changes in the shape of the polymer that allows new control over its optical properties. A metamaterial is a material that has been designed to have properties that would not normally be found in nature, usually through the use of geometrical structures that are larger than atoms but still microscopic. Optical metamaterials are perhaps the most famous of these materials, mainly due to Imperial College’s metamaterial-based ‘invisibility cloak’, the theory of which was developed by Professor John Pendry in the Department of Physics.
The ‘dip-pen nanolithography’ deposition technique works by coating what is essentially an atomically thin pen tip with a solvent, which in this case swells upon contact with the substrate. This swelling induces a change in the geometrical conformation of the polymer such that adjacent molecular segments are pointing in different directions. This is what gives the optical properties of the deposited film directional dependence. Control of this directional dependence may one day lead to LED sources that emit light in a tightly controlled direction as opposed to at many different angles.
It is also hoped that such detailed control over optical properties may find application in other technologies as diverse as optical waveguides, lasers or output and input couplers for photonic devices.
Andrew McMahon is a first year PhD student studying physics
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