October 28, 2021

I, Science

The science magazine of Imperial College

Andrew McMahon looks at a new optical metamaterial
Classic dip pen nanolithography
Classic dip pen nanolithography

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 molecules 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 Colleges 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.

Perevedentsev, A. et al (2015) Dip-pen patterning of poly(9,9-dioctylfluorene) chain-conformation-based nano-photonic elements. Nature Communications 6, Article number: 5977, doi:10.1038/ncomms6977

Andrew McMahon is a first year PhD student studying physics

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