Browsing by Author "Nasser, H."
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Article Citation Count: 16Optical characteristics of Bi12SiO20 single crystals by spectroscopic ellipsometry(Elsevier Sci Ltd, 2020) Işık, Mehmet; Delice, S.; Nasser, H.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.; Department of Electrical & Electronics EngineeringStructural and optical characteristics of Bi12SiO20 single crystal grown by the Czochralski method were investigated by virtue of X-ray diffraction (XRD) and spectroscopic ellipsometry measurements. XRD analysis indicated that the studied crystal possesses cubic structure with lattice parameters of a = 1.0107 nm. Spectral dependencies of several optical parameters like complex dielectric constant, refractive index, extinction and absorption coefficients were determined using ellipsometry experiments performed in the energy region of 1.2-6.2 eV. The energy band gap of Bi12SiO20 crystals was found to be 3.25 eV by utilizing absorption coefficient analysis. Moreover, critical point energies were calculated as 3.54, 4.02, 4.82 and 5.58 eV from analyses of the second energy derivative spectra of the complex dielectric constant.Article Citation Count: 0Optical constants and critical point energies of (AgInSe2)0.75-(In2Se3)0.25 single crystals(Springer, 2020) Işık, Mehmet; Nasser, H.; Guseinov, A.; Gasanly, N. M.; Department of Electrical & Electronics EngineeringAgInSe2 and In2Se3 are two attractive semiconducting materials for various technological applications especially for photovoltaic applications. In the present study, structural and optical properties of (AgInSe2)(x)-(In2Se3)(1-x) crystals for composition of x = 0.75 corresponding to chemical formula of Ag3In5Se9 were characterized by X-ray diffraction, energy-dispersive spectroscopy, room temperature transmission, and ellipsometry experiments. The transmittance spectrum was analyzed to reveal energy band gap. The derivative spectrophotometry analysis resulted in band gap energy of 1.22 eV. The spectra of complex dielectric function, refractive index and extinction coefficient were presented between 1.6 and 6.2 eV from the outcomes of ellipsometry analyses. Critical point energies have been determined using the derivative analyses of dielectric function. Five critical points at 2.70, 3.30, 4.05, 4.73, and 5.42 eV were revealed from the analyses. Crystal structure and atomic composition in semiconducting compound were also reported in the present work. The obtained results were compared with those reported for constituent compounds.Article Citation Count: 3Optical properties of Cu3In5S9 single crystals by spectroscopic ellipsometry(Elsevier Gmbh, 2018) Işık, Mehmet; Nasser, H.; Ahmedova, F.; Guseinov, A.; Gasanly, N. M.; Department of Electrical & Electronics EngineeringCu3In5S9 single crystals were investigated by structural methods of x-ray diffraction and energy dispersive spectroscopy and optical techniques of ellipsometry and reflection carried out at room temperature. The spectral dependencies of optical constants; dielectric function, refractive index and extinction coefficient, were plotted in the range of 1.2-6.2 eV from ellipsometric data. The spectra of optical constants obtained from ellipsometry analyses and reflectance spectra presented a sharp change around 1.55 and 1.50 eV, respectively, which are associated with band gap energy of the crystal. The critical point (interband transition) energies were also found from the analyses of second-energy derivative of real and imaginary components of dielectric function. The analyses indicated the presence of four critical points at 2.73, 135, 4.04 and 4.98 eV.