Materials scientists from the USA have found a way to make a thin layer of quantum dots on a photonic crystal surface, thereby creating a stable material with enhanced emission properties.
A question that has challenged materials scientists for some time is how to integrate light-emitting materials like quantum dots with complementary photonic materials that couple well with the quantum dots. A quantum dot is a structure whose properties depend critically on its shape and size, usually a nanoparticle. Quantum dots are used widely as emissive markers and have important fluorescence properties; they spontaneously emit. A photonic crystal is an ordered arrangement of small particles that affects the motion of photons of light passing through it in a certain way. Such a combination should enhance emission from the quantum dots and make them easier to use in a broad range of applications.
The team, from University of New Mexico and headed by Jeff Brinker, used a technique that they had previously developed that combines molecular self-assembly with evaporative assembly to create nanoparticle arrays on a surface. They assemble nanoparticles at a polymer solution–air interface and then transfer this array to a photonic crystal surface using a “picking” or “lifting” procedure. They then simply remove the solvent and are left with a monolayer of quantum dots on the photonic crystal surface. Depending on the transferral procedure used, the properties of the resulting layers can be tuned.
The new method is better than spin-coating as it creates a more uniform film, and is much quicker than growing a layer of quantum dot nanocrystals directly onto the surface. It also has some advantages over the use of templates as a much higher density of quantum dots can be achieved with the new technique.
Control over the emissive properties of quantum dots is necessary in many applications such as lasers, light-emitting diodes, single-photon sources for quantum information, and solar-energy harvesting. This new technique could help to bring down the costs of such devices, as it is simpler than existing fabrication methods. The high density and ordering of the quantum dot arrays made in this way could also open up possible new applications as they are different from previously produced nanoparticle-surface arrays.
