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Article Citation - WoS: 14Citation - Scopus: 15Structural and Optical Properties of Ga2se3< Crystals by Spectroscopic Ellipsometry(Springer, 2019) Guler, I.; Isik, M.; Gasanly, N. M.; Gasanova, L. G.; Babayeva, R. F.Optical and crystalline structure properties of Ga2Se3 crystals were analyzed utilizing ellipsometry and x-ray diffraction (XRD) experiments, respectively. Components of the complex dielectric function (epsilon=epsilon(1)+i epsilon(2)) and refractive index (N=n+ik) of Ga2Se3 crystals were spectrally plotted from ellipsometric measurements conducted from 1.2eV to 6.2eV at 300K. From the analyses of second-energy derivatives of epsilon(1) and epsilon(2), interband transition energies (critical points) were determined. Absorption coefficient-photon energy dependency allowed us to achieve a band gap energy of 2.02eV. Wemple and DiDomenico single effective oscillator and Spitzer-Fan models were accomplished and various optical parameters of the crystal were reported in the present work.Article Citation - WoS: 1Citation - Scopus: 1Structural and Optical Properties of Thermally Evaporated Ga-In Thin Films(World Scientific Publ Co Pte Ltd, 2014) Isik, Mehmet; Gullu, Hasan HuseyinIn this paper, structural and optical properties of Ga-In-Se (GIS) thin films deposited by thermal evaporation technique have been investigated. The effect of annealing was also studied for samples annealed at temperatures between 300 degrees C and 500 degrees C. X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy have been used for structural characterization. It was reported that increase of annealing temperature results with better crystallization and chemical composition of the films were almost same. Optical properties of the films were studied by transmission measurements in the wavelength range of 320-1100 nm. The direct bandgap transitions with energies in the range of 1.52 eV and 1.65 eV were revealed for the investigated GIS films. Photon energy dependence of absorption coefficient showed that there exist three distinct transition regions for films annealed at 400 degrees C and 500 degrees C. The quasicubic model was applied for these transitions to calculate crystal-field splitting and spin-orbit splitting energy values.Article Citation - WoS: 5Citation - Scopus: 4Properties of Se/Inse Thin-Film Interface(Springer, 2016) Qasrawi, A. F.; Qasrawı, Atef Fayez Hasan; Kayed, T. S.; Elsayed, Khaled A.; Kayed, Tarek Said; Qasrawı, Atef Fayez Hasan; Kayed, Tarek Said; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringSe, InSe, and Se/InSe thin films have been prepared by the physical vapor deposition technique at pressure of similar to 10(-5) torr. The structural, optical, and electrical properties of the films and Se/InSe interface were investigated by means of x-ray diffraction (XRD) analysis, ultraviolet-visible spectroscopy, and current-voltage (I-V) characteristics. XRD analysis indicated that the prepared InSe films were amorphous while the Se films were polycrystalline having hexagonal structure with unit cell parameters of a = 4.3544 and c = 4.9494 . Spectral reflectance and transmittance analysis showed that both Se and InSe films exhibited indirect allowed transitions with energy bandgaps of 1.92 eV and 1.34 eV, respectively. The Se/InSe interface exhibited two energy bandgaps of 0.98 eV and 1.73 eV above and below 2.2 eV, respectively. Dielectric constant values were also calculated from reflectance spectra for the three layers in the frequency range of 500 THz to 272 THz. The dielectric constant exhibited a promising feature suggesting use of the Se/InSe interface as an optical resonator. Moreover, the Au/Se/InSe/Ag heterojunction showed some rectifying properties that could be used in standard optoelectronic devices. The ideality factor and height of the energy barrier to charge carrier motion in this device were found to be 1.72 and 0.66 eV, respectively.Article Citation - WoS: 3Citation - Scopus: 4In Situ Observation of Heat-Assisted Hexagonal-Orthorhombic Phase Transitions in Se/Ag Sandwiched Structures and Their Effects on Optical Properties(Springer, 2019) Qasrawi, A. F.; Aloushi, Hadil D.In this work, two selenium layers of 500-nm thickness, nano-sandwiched with Ag nanosheets of 100-nm thickness (Se/Ag/Se), are subjected to in situ monitoring of the structural and optical transitions during heating over a temperature range of 303-473 K by x-ray diffraction and ultraviolet-visible light spectrophotometry, respectively. The Se/Ag/Se thin films are observed to exhibit a transformation from an amorphous to a polycrystalline phase at 343 K. Increasing the temperature above 363 K enhances the crystallinity of the hexagonal phase, reduces the microstrain, increases the crystallite size and reduces the defect density. Accordingly, the optical absorption spectra are redshifted upon heating. The redshift is accompanied by a transition in the energy band gap from 2.03 eV to 1.85 eV as the material structural phase is transformed from amorphous to polycrystalline. Increasing the temperature causes the energy band gap to shrink. Another permanent phase transformation from hexagonal to orthorhombic is detected when the Se/Ag/Se system is allowed to cool. Scanning electron microscopy images show that the phase transformation converts the grains of Se/Ag/Se films from wire-shaped to nanotubes. The second phase transformation causes a blueshift in the absorption coefficient spectra and increases the energy band gap. The structural and optical parameter enhancements achieved via heating render the Se thin films more suitable for optoelectronic applications.Article Citation - WoS: 2Citation - Scopus: 1Hydrogen Implantation Effects on the Electrical and Optical Properties of Inse Thin Films(Tubitak Scientific & Technological Research Council Turkey, 2012) Qasrawi, Atef Fayez; Ilaiwi, Khaled Faysal; Polimeni, AntonioThe effects of hydrogen ion implantation on the structural, electrical and optical properties of amorphous InSe thin films have been investigated. X-ray diffraction analysis revealed no change in the structure of the films. An implantation of 7.3 x 10(18) ions/cm(2) decreased the electrical conductivity by three orders of magnitude at 300 K. Similarly, the conductivity activation energy, which was calculated in the temperature range of 300-420 K, decreased from 210 to 78 meV by H-ion implantation. The optical measurements showed that the direct allowed transitions energy band gap of amorphous InSe films has decreased from 1.50 to 0.97 eV by implantation. Furthermore, significant decreases in the dispersion and oscillator energy, static refractive index and static dielectric constants are also observed by hydrogen implantation.Article Citation - WoS: 4Citation - Scopus: 4Optical Characterization of Ga2ses Layered Crystals by Transmission, Reflection and Ellipsometry(World Scientific Publ Co Pte Ltd, 2015) Isik, Mehmet; Gasanly, NizamiOptical properties of Ga2SeS crystals grown by Bridgman method were investigated by transmission, reflection and ellipsometry measurements. Analysis of the transmission and reflection measurements performed in the wavelength range of 400-1100 nm at room temperature indicated the presence of indirect and direct transitions with 2.28 eV and 2.38 eV band gap energies. Ellipsometry measurements were carried out in the 1.2-6.0 eV spectral region to get information about optical constants, real and imaginary parts of the pseudodielectric function. Moreover, the critical point (CP) analysis of the second derivative spectra of the pseudodielectric constant in the above band gap region was accomplished. The analysis revealed the presence of five CPs with energies of 3.87, 4.16, 4.41, 4.67 and 5.34 eV.Article Citation - WoS: 50Citation - Scopus: 51Elemental Sulfur-Based Polymeric Materials: Synthesis and Characterization(Wiley-blackwell, 2016) Salman, Mohamed Khalifa; Karabay, Baris; Karabay, Lutfiye Canan; Cihaner, AtillaNew elemental sulfur-based polymeric materials called poly(sulfur-random-divinylbenzene) [poly(S-r-DVB)] were synthesized by ring opening polymerization via inverse vulcanization technique in the presence of a mixture of o-, m-, and p-diviniylbenzene (DVB) as a cross-linker. A clear yellow/orange colored liquid was obtained from the elemental sulfur melted at 160 degrees C and then by adding various amounts of DVB to this liquid directly via a syringe at 200 degrees C viscous reddish brown polymeric materials were obtained. The copolymers are soluble in common solvents like tetrahydrofuran, dichloromethane, and chloroform, and they can be coated on any surface as a thin film by a spray coating technique. The characterization of the materials was performed by using nuclear magnetic resonance, fourier transform infrared, and Raman spectroscopies. The morphological properties were monitored via scanning electron microscope technique. Thermal analysis showed that an increase in the amount of DVB in the copolymers resulted in an increase in the thermal decomposition temperature. On the other hand, poly(S-r-DVB) copolymers exhibited good percent transmittance as 50% T between 1500 and 13,000 nm in electromagnetic radiation spectrum, which makes them good candidates to be amenable use in military and surveillance cameras. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43655.
