Determination of the dielectric tensor function of crystals with arbitrary structure and orientation based on reflectance measurements

• Applicant: Privatdozent Dr. Thomas Mayerhöfer
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2012 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 229614732

The goal of the determination of oscillator parameters of a single crystal (dispersion analysis) is twofold. First the knowledge of these parameters can be used to analyze the structure properties relationships of the crystal and, second, as the parameters describe the function of the dielectric tensor in a certain spectral range, to calculate optical properties like reflectance, transmittance and scattering for single crystals and polycrystalline textured or randomly oriented materials.Recently, dispersion analysis based on the evaluation of reflectance measurements was extended to triclinic crystals and can therefore be applied to all crystals regardless their crystal structure. However, apart from the triclinic (and, trivially, cubic) single crystals, all other species need to be oriented prior to dispersion analysis. This orientation is usually carried out with help of X-ray diffraction methods. In a second step the oriented crystals need to be cut along and perpendicular to certain crystal axes and planes.The goal of the project is to develop a procedure for which an orientation step is not necessary and, eventually, also the determination of crystal structure and orientation is determined by reflectance spectroscopy with a subsequent dispersion analysis.In the first project phase dispersion analysis will be further developed to the point where it is possible to carry it out without prior orientation of a crystal if its crystal structure is known. The goal of the second phase consist of adapting and enhancing the oscillator model for triclinic crystals and thereby dispersion analysis in a way that knowledge of neither crystal structure nor orientation is a priori necessary to successfully conduct a dispersion analysis.

• DFG Programme: Research Grants
• International Connection: North Macedonia
• Participating Persons: Professor Dr. Vladimir Ivanovski; Reinhard Uecker, Ph.D.