Researchers use a nib to change optical properties of polymer semiconductors

Scientists at Imperial College London have developed a way to manipulate the optical properties of polymers by drawing patterns with a solvent 'ink'. The approach is said to allow more precise control over how these materials interact with light and could have application in all kinds of devices that emit, detect and control light. One example offered by the research team is the ability to make tiny LEDs that emit light in one direction only, rather than across a broad range of angles, thereby offering the prospect of compact light source arrays for medical diagnostic applications.

The researchers used a tiny pen to draw patterns with a solvent on a thin film of polymer semiconductor. The solvent changes the shape of a selection of chain segments from a disordered state to ordered rigid strands. This change in structure alters the way in which the material interacts with light, changing its refractive index as well as the colour of light emitted.

Professor Donal Bradley, director of the Centre for Plastic Electronics at Imperial College London, said: "Usually we use lenses or mirrors to change the direction of light. This method lets us manipulate a light source itself to tightly control the direction of light that it emits. The material adopts the desired structure naturally – it just requires a little encouragement to do so."

The approach is said to allow scientists to alter these properties on a much smaller scale than they could before – over distances shorter than the wavelength of light. The researchers expect this will make it possible to build a variety of novel structures leading to new and more efficient devices.

Graham Pitcher

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