"The precision and yield of the expected structure is extremely high, and the degree of control achieved is greater than in any previous attempt to pattern metallic nanoparticles in a defined geometry," says coauthor Professor Friedrich Simmel, a physicist at the Technical University of Munich. By varying the size, disposition and composition of the nanoparticles or altering other features of the water-soluble structures, the investigators can customize the impact of the material on light rays passing through it.
For instance, by arranging the gold particles in right or left-handed helices, the properties of the transmitted light are altered accordingly. The magnitude of the optical response was found to be markedly dependent on the size of the particles, and their precise chemical nature also has a significant influence on how they interact with incident light. Thus, if the gold particles are coated with silver, the position of the optical resonance is shifted from the red to the blue range of the spectrum.
The phenomenon of circular dichroism can be used to characterize the optical activity of materials. It is measured using two light beams of defined wavelength which are circularly polarized in opposite senses and modulated in different ways by passage through the material. When the response of a given sample of the metamaterial was determined at various wavelengths, the results were found to agree with calculations based on a theoretical model. Hence, the model can be used to design materials that modulate light in specific ways. "We will now test whether we can also alter the refractive index of our materials," says Liedl. "Materials with a negative index of refraction could, for instance, serve as the basis for novel optical lens systems."(NIM/suwe)
|Contact: Dr. Kathrin Bilgeri|