Active and low loss nano photonics (ActiveNP)

Final Report Summary - ACTIVENP (Active and low loss nano photonics (ActiveNP))

The project “ActiveNP” aimed at designing novel hybrid nano-photonic devices comprising metallic nanostructures of unusual shape and active elements such as dye molecules. Such hybrid devices are envisaged to play an important future role in nano-photonics for instance to be used in photonic nanocircuits or in biodiagnostics. A major challenge for the use of metallic nanostructures in optics is their intrinsic Ohmic loss. In contrast, dye molecules in their excited state are intrinsic sources of energy. The project was inspired by the idea of bringing both together and to compensate losses in metallic photonic devices such as metamaterials by active materials.

We made substantial progress in developing novel plasmonic nanostructures of unusual shape such as self-assembled sponge-like gold nanoparticles, or gold-nanostars, silver enhanced nanostars and metallic nanoparticles, covered with insulating silica shells of less than 10 nm, produced by whet chemical synthesis. Further, square-cm large nano-patterned layers were produced such as self-assembled hexagonal patterns of silver nanocaps and nanoimprinted fishnet-like silver nanostructures. These structures show quite unusual plasmonic behavior: For instance, the optically spectroscopic response of the nanosponges is dominated by internal electromagnetic hot spots, which are potentially important for bio-chemical sensing applications such as Raman scattering or surface enhanced infrared spectroscopy. As a second example, large area nanoimprinted fishnet structures turned out to be suitable as nanometer-thin polarization-rotating mirrors. Such devices could find further use in micro-optic systems.

When combining the plasmonic structures with sources of optical energy (active materials) such as organic fluorophores or semiconducting quantum dots, several interesting effects could be observed: For instance, polystyrene spheres doped with dye molecules and overgrown by silver caps showed tight interactions of the plasmonic modes of the metallic caps and the fluorescence emission. This leads to a reshaping of the dye molecules’ emission spectra and simultaneously to a spatial redirection of the fluorescence emission. This can potentially be useful in light emitting devices or, if the path of light is reversed, to concentrate incoming sunlight towards an absorber and hence to improve solar cells. Further, several schemes of lasers were realized which do not rely on the usual optical feedback by plane mirrors, but by a feedback due to multiple scattering at randomly distributed gold nanostars. Both, organic molecules and semiconductor nanocrystals were shown to be suitable active materials for such type of “random lasers”. Further, it was shown that the luminance of organic light emitting diodes can be substantially improved by adding silver-enhanced gold nanostars which are electrically passivated by a sub-10 nm silica shell. This knowledge will in future be used to also improve organic solar cells in a follow-up project.

An interdisciplinary team of PhD students and PostDocs originating from eight nations has worked on the project where they joined not only their diverse cultural background but also their different scientific knowledge covering experimental and theoretical physics, chemistry and materials science.

Final Report Summary - ACTIVENP (Active and low loss nano photonics (ActiveNP))

Diese Seite teilen

Herunterladen