Optical properties of solids and spectroscopy of solids
By using spectroscopic techniques (Raman, IR, absorption, Photoluminescence) and the synergy of theoretical calculations (phenomenological models, first-principles calculations, group theory) the optical properties of a wide range of materials (semiconductors, fullerenes, carbon nanotubes, garnets, low-dimensional materials etc.) are studied. These techniques and theoretical methods are utilized for materials characterization (identification of polytypes and phases, crystallinity, presence of mechanical stress/strain, chemical functionalization, electronic doping etc.) as well as for the study of fundamental physical phenomena (electron-phonon interaction, Kohn anomalies, immediate neighboring interactions etc.).
Moreover, the influence of external perturbations (temperature, uniaxial or biaxial mechanical deformation, hydrostatic pressure, electrochemical doping etc.) modifies drastically the optical properties of a material providing, thus, information on the physical phenomena themselves and allows the investigation of structural stability and the study of pressure induced structural or electronic phase transitions of materials.
Study of the nanostructure (nearest neighbor distances, coordination numbers and bond angles) as well as optical properties (density of unoccupied states) in the soft and hard x-ray spectral region using x-ray absorption spectroscopies EXAFS & NEXAFS.
Elemental mapping using the x-ray fluorescence spectroscopy (XRF mapping) and micro XAFS. The samples under study are:
i) compounds of Si (mainly SiNx)
ii) group III nitrides (GaN, AlN, InN and their alloys)
iii) glasses and glass ceramics containing solid wastes (information on the sample preparation can be found in the web page of WFENV-NET http://web.auth.gr/wfenv-net
iv) biological samples for the determination of the trace element concentration
Moreover, inelastic X-ray (and alternatively neutron) scattering for the study of dispersion curves and the density of states of crystalline solids can be conducted.