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Citation - WoS: 1
Citation - Scopus: 1
Characterization of Pbmo_0.3w_{0.7< Crystal: a Potential Material for Photocatalysis and Optoelectronic Applications}
(Wiley-v C H verlag Gmbh, 2024) Isik, Mehmet; Gasanly, Nizami Mamed
PbMo0.3W0.7O4 semiconductor crystal, which contains the balanced ratios of Mo and W, is grown for the first time by Czochralski method. The structural and optical properties of the crystal are investigated in detail in the present study. Structural analysis shows that crystal has tetragonal structure like PbMoO4 and PbWO4 compounds. The optical characteristics are studied by transmission, Raman, FTIR and photoluminescence methods. The bandgap energy is found to be 3.18 eV, and the positions of the conduction and valence bands are determined. The vibrational characteristics are studied by means of Raman and FTIR spectroscopy techniques. Photoluminescence spectrum presents three peaks around 486, 529, and 544 nm which fall into the green emission spectral range. Taking into account the properties of the compound, it is stated that PbMo0.3W0.7O4 (or Pb(MoO4)(0.3)(WO4)(0.7)) has the potential to be used in water splitting applications and optoelectronic devices that emit green light.
Citation - WoS: 5
Citation - Scopus: 5
Optical Properties of Tlga_xin_{1-x< Mixed Crystals (0.5 ≤ x ≤ 1) by Spectroscopic Ellipsometry, Transmission, and Reflection}
(Taylor & Francis Ltd, 2014) Isik, M.; Delice, S.; Gasanly, N. M.
The layered semiconducting TlGaxIn1-xSe2-mixed crystals (0.5 <= x <= 1) were studied for the first time by spectroscopic ellipsometry measurements in the 1.2-6.2 eV spectral range at room temperature. The spectral dependence of the components of the complex dielectric function, refractive index, and extinction coefficient were revealed using an optical model. The interband transition energies in the studied samples were found from the analysis of the second-energy derivative spectra of the complex dielectric function. The effect of the isomorphic cation substitution (indium for gallium) on critical point energies in TlGaxIn1-xSe2 crystals was established. Moreover, the absorption edge of TlGaxIn1-xSe2 crystals have been studied through the transmission and reflection measurements in the wavelength range of 500-1100 nm. The analysis of absorption data revealed the presence of both optical indirect and direct transitions. It was found that the energy band gaps decrease with the increase of indium content in the studied crystals.
Citation - WoS: 14
Citation - Scopus: 15
Structural and Optical Properties of Ga₂se_{3< 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.
Citation - WoS: 1
Citation - Scopus: 1
Structural and Optical Properties of Thermally Evaporated Ga-In Thin Films
(World Scientific Publ Co Pte Ltd, 2014) Isik, Mehmet; Gullu, Hasan Huseyin
In 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.
Citation - WoS: 5
Citation - Scopus: 5
Growth and Temperature Tuned Band Gap Characteristics of Nabi(moo₄)_{2< Single Crystal}
(Iop Publishing Ltd, 2023) Isik, M.; Guler, I; Gasanly, N. M.
Structural and optical properties of double sodium-bismuth molybdate NaBi(MoO4)(2) semiconductor compound was investigated by x-ray diffraction, Raman and transmission experiments. From the x-ray diffraction experiments, the crystal that has tetragonal structure was obtained. Vibrational modes of the crystal were found from the Raman experiments. Transmission experiments were performed in the temperature range of 10-300 K. Derivative spectroscopy analysis and absorption spectrum analysis were performed to get information about the change in band gap energy of the crystal with temperature. It was observed that the band gap energies of the crystal at different temperatures obtained from these techniques are well consisted with each other. By the help of absorption spectrum which was obtained from transmission measurements performed at varying temperatures, absolute zero value of the band gap and average phonon energy as 3.03 +/- 0.02 eV and Eph = 24 +/- 0.2 meV, respectively. Moreover, based on absorption spectrum analysis the Urbach energy of the crystal was obtained as 0.10 eV.
Citation - WoS: 4
Citation - Scopus: 4
Physical Properties of Neodymium Tin Oxide Pyrochlore Ceramics
(de Gruyter Poland Sp Zoo, 2017) Saleh, Adli A.; Qasrawi, A. F.; Yumusak, G.; Mergen, A.
In this work, physical properties of neodymium tin oxide pyrochlore ceramics prepared by solid state reaction technique are investigated by means of X-ray diffraction, scanning electron microscopy, ultraviolet-visible light (UV-Vis) spectrophotometry and temperature dependent electrical resistivity measurements. The pyrochlore is observed to have a cubic FCC crystal lattice with lattice parameter of 10.578 angstrom. The planes of the cubic cell are best oriented in the [2 2 2] direction. From the X-ray, the UV-Vis spectrophotometry and the electrical resistivity data analysis, the grain size, strain, dislocation density, optical and thermal energy band gaps, localized energy band tail states and resistivity activation energies are determined and discussed. The pyrochlore is observed to have an optical energy band gap of similar to 3.40 eV. This value corresponds to 365 nm UV light spectra which nominates the neodymium tin oxide pyrochlore ceramics for the use as UV sensors.
Citation - WoS: 10
Citation - Scopus: 11
Dispersive Optical Constants of Thermally Deposited Agin₅s_{8< Thin Films}
(Elsevier Science Sa, 2008) Qasrawi, A. F.
Agln(5)S(8) thin films were obtained by the thermal evaporation of Agln(5)S(8) crystals onto ultrasonically cleaned glass substrates. The films are found to exhibit polycrystalline cubic structure. The calculated lattice parameter of the unit cell (a) is 10.78 angstrom. The transmittance data of the as grown films which was recorded at 300 K in the incidence wavelength (lambda) range of 320-1000 nm are used to calculate the refractive, n(lambda). The transmittance and reflectance data are also used to calculate the absorption coefficient of the as grown Agln5S8 thin films. The fundamental absorption edge is found to be corresponding to a direct allowed transitions energy band gap. This band-to-band transition energy is found to be 1.78 eV and it is consistent with that reported for Agln(5)S(8) single crystals. (c) 2007 Elsevier B.V. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 4
Properties 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 Engineering
Se, 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.
Citation - WoS: 3
Citation - Scopus: 4
In 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.
Citation - WoS: 32
Citation - Scopus: 32
Temperature Dependence of the Band Gap, Refractive Index and Single-Oscillator Parameters of Amorphous Indium Selenide Thin Films
(Elsevier Science Bv, 2007) Qasrawi, A. F.
InSe thin films are obtained by evaporating InSe crystal onto ultrasonically cleaned glass substrates under pressure of similar to 10(-5) Torr. The structural and compositional analysis revealed that these films are of amorphous nature and are atomically composed of similar to 51% In and similar to 49% Se. The reflectance and transmittance of the films are measured at various temperatures (300-450 K) in the incident photon energy range of 1.1-2.1 eV. The direct allowed transitions band gap - calculated at various temperatures - show a linear dependence on temperature. The absolute zero value band gap and the rate of change of the band gap with temperature are found to be (1.62 +/- 0.01) eV and -(4.27 +/- 0.02) x 10(-4) eV/K, respectively. The room temperature refractive index is estimated from the transmittance spectrum. The later analysis allowed the identification of the static refractive index, static dielectric constant, oscillator strength and oscillator energy. (c) 2006 Elsevier B.V. All rights reserved.

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