The project C2 focuses on the theoretical and experimental study of light scattering by multiscale materials, whose building blocks on the nanoscale are dielectric multilayers which are arranged on the mesoscale as spheres or cylinders which assume an effective radially anisotropic permittivity (Fig. 1 a and b). On the microscale such particles are then arranged in a disordered or crystalline manner, exhibiting either photonic glass or photonic crystal structure, respectively. On the macroscale photonic glasses and photonic crystals are arranged in film geometry.
Dielectric spheres and cylinders with radially anisotropic permittivity have been studied theoretically by several research groups in the past years. It was proven that, in such a particle, the magnetic dipole response is unaffected by the radial permittivity component, while the electric dipole depends on both, the radial and the tangential one. This finding was used to show the generation of new scattering properties, like strong forward scattering or backscattering suppression. However, previous research has been limited to the theoretical study of particles with high anisotropy and unrealistic refractive indices.
In this project we focus on particles with weak anisotropy, which can be manufactured from conventional dielectric materials such as SiO2, Al2O3 and TiO2. We will prepare radially anisotropic particles from radial configurations on the nanoscale, for example with multilayered spheres and cylinders or a concentric arrangement of liquid crystals in a cylindrical pore. The difference between radial and azimuthal permittivity component can be varied from 0.1 to 0.5. We want to study the scattering theoretically using the first-order Born approximation and Mie theory. In parallel, we will carry out the experimental study of the scattering properties. Multilayered spheres and cylinders will be fabricated in project C8 and assembled in project C4. Further, materials with cylindrical pores will be filled with liquid crystals in radial arrangements in project C10. We will use angle-resolving scattering setups and spectrometers to study the optical properties of particles and assemblies.
Besides the mere realization and theoretical as well as experimental characterization of radially anisotropic nanoscopic entities arranged to novel macroscopic scattering media, one goal of the project is to provide additional spectral selectivity of disordered materials via controlled radial anisotropy of constituent particles. Better structural colors are envisaged, especially in the long wavelength range, such as red color.
Fig. 1: The effective permittivity of radially anisotropic sphere (a) or a cylinder (b) differs in radial and tangential direction. Such entities can be realized as multilayered spheres (c) or multilayered cylinders or cylindrical pores (d).
|Prof. Dr. rer. nat. Manfred Eich,
|Dr. rer. nat. Alexander Petrov,
thermal barrier coatings
... and more on the list of publications.