Raman spectroscopy, IR, absorption

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.

• Indicative activities:
  1. Study of optical properties under normal conditions, high pressure and as a function of temperature of materials such as semiconductors (ΙΙΙ-V, II-VI), fullerenes and related compounds, chemically modified carbon nanotubes and scheelite compounds (ABO₄, Α = Ca, Sr, Ba and B = W, Mo).
  2. Study of the optical properties of two-dimensional materials such as graphene (single or multilayers), BN, transition metal dichalcogenides (MoS₂, WS₂, Mo_1-xW_xS₂, MoSe₂) as a function of their interaction with various substrates, physical or chemical electronic doping, mechanical deformation and hydrostatic pressure.
  3. Study of III-V nitrides (AlN, Gan, InN and their alloys) using Raman spectroscopy: effect of ion implantation and doping as well as of the stresses induced during the epitaxial growth.
  4. Lattice dynamics of the rare earth aluminum and gallium garnets in a crystal form and as solid solutions (RE₃Al₅O₁₂ and RE₃Ga₅O₁₂, RE=rare earth).
• Equipment:
  1. Raman and photoluminescence set-up consisted of a triple monochromator (DILOR ΧΥ) with gratings of 1800 lines/mm and a CCD (EG&G 1433-C) liquid-nitrogen-cooled detector.
  2. Raman spectrometer RAMALOG 5 equipped with a Peltier-cooled photomultiplier tube with GaAs photocathode and a triple-monochromator that covers the wavelength range 12000 – 28000 cm^-1 (8500-3500Å), fully automated and PC controlled.
  3. Two Ar⁺ Lasers of Spectra Physics 2W.
  4. One Kr Laser of Lexel 1.5 W.
  5. One cryostat accompanied by a diffusion pump of Cryogenic that works down to 20 K.
  6. Gas membrane driven diamond anvil cells, micro-tensiometers for the application of mechanical deformation (uniaxial, biaxial).