EPJ B Highlight - From stained glass to novel optical effect

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Published on 13 January 2015

Physicists investigate hybrid nanostructures made of semiconductor and metal components, yielding novel electronic and optical characteristics when exposed to light

Coloured stained-glass windows in churches typically contain metallic nanoparticles. They illustrate how light interacts with matter in a specific way at nanoscales. Depending on the material, different types of excitations arise within the inner structure of the material. By combining two different nanostructures, physicists expect the best electronic and optical response from each material. A team of Austrian scientists has just produced a model describing the optical properties of a matchstick-shaped hybrid nanoparticle, made of a cadmium sulphide semiconductor rod attached to a metallic gold cap. The results have been published in EPJ B by physicist Jakob Ebner and colleagues from the Karl Franzens University in Graz. Similar light-matter interactions have been observed in related systems, such as graphene. Better understanding such interactions could ultimately help in enhancing the sensitivity of chemical or biological detectors, as well as in increasing the efficiency of solar cells.

In this study, the authors focus on the interplay between two types of excitation. First, the excitation found in the semiconductor, called excitons, which are a quasi-particle constituted of strongly bound electron-hole pairs. Second, the excitations of the metallic component, called plasmons. These are collective electron oscillations taking place at the metal surface, leading to pronounced light scattering at specific frequencies.

Ebner and colleagues then study the light-matter coupling in the hybrid nanostructure in a unique theoretical model. They demonstrate that the way the hybrid produces light is complex and involves various electronic coupling mechanisms. As a result, the authors predict novel excitations, referred to as plexcitons. These represent the best of the two worlds of semiconductor optics and plasmonics, combining the rich variety of active semiconductor materials with the unique light emission properties of plasmonic nanoparticles.