Browsing by Author "Isik, Mehmet"

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Citation - WoS: 1
Citation - Scopus: 1
Analysis of Glow Curve of Gas_0.5se_{0.5< Single Crystals}
(Elsevier Science Bv, 2015) Isik, Mehmet; Delice, Serdar; Gasanly, Nizami; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Characterization of shallow trapping centers in GaS0.5Se0.5 crystals grown by a Bridgman method was carried out in the present work using thermoluminescence (TL) measurements performed in the low temperature range of 10-300 K. The activation energies of the trapping centers were obtained under the light of results of various analysis methods. The presence of three trapping centers located at 6, 30 and 72 meV was revealed. The analysis of the experimental glow curve gave reasonable results under the model that assumes slow retrapping which states the order of kinetics as b=1. Heating rate dependence of the observed TL peaks was studied for the rates between 0.4 and 1.0 K/s. Distribution of the traps was also investigated using an experimental technique based on the thermal cleaning of centers giving emission at lower temperatures. The distributed levels with activation energies increasing from 6 to 136 meV were revealed by increasing the stopping temperature from 10 to 52 K. (C) 2015 Elsevier B.V. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 2
Analysis of Optical Constants and Temperature-Dependent Absorption Edge of Gas_0.75se_{0.25< Layered Crystals}
(Pergamon-elsevier Science Ltd, 2017) Isik, Mehmet; Gasanly, Nizami; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
GaS0.75Se0.25 single crystals were optically characterized through transmission and reflection measurements in the wavelength range of 450-1000 nm. Derivative spectrophotometry analyses on temperature dependent transmittance spectra showed that band gap energies of the crystal increase from 239 eV (T=300 K) to 2.53 eV (T=10 K). Band gap at zero temperature, average phonon energy, electron phonon coupling parameter and rates of change of band gap energy with temperature were found from the temperature dependences of band gap energies under the light of different models reported in literature. Furthermore, the dispersion of room temperature refractive index was discussed in terms of single effective oscillator model. The refractive index dispersion parameters, namely oscillator and dispersion energies, zero-frequency refractive index, were determined as a result of analyses. (C) 2017 Elsevier Ltd. All rights reserved.
Citation - WoS: 7
Citation - Scopus: 12
Bifunctional Praseodymium-Doped Sns2 Thin Films for Photocatalytic and Antibacterial Applications
(Elsevier, 2024) Ech-Chergui, Abdelkader Nebatti; Bennabi, Farid; Isik, Mehmet; Khane, Yasmina; Garcia, Francisco Jose Garcia; Kadari, Ali Sadek; Amrani, Bouhalouane; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
This paper introduces a novel application of bifunctional Pr-doped SnS2 thin films, demonstrating their efficacy in both photocatalytic degradation of dye and antibacterial activities. The thin films were fabricated using an eco-friendly spray-coated method, encompassing undoped and Pr-doped SnS2 variations. The study comprehensively examines the structural, morphological, chemical, photocatalytic, and antibacterial characteristics of these films. The crystal structure of both undoped and Pr-doped SnS2 thin films exhibited hexagonal patterns, prominently favouring the growth in (1 0 1) orientation. Notably, an increase in crystallite size was observed with higher levels of Pr-doping. Raman spectroscopy analysis highlighted a distinct peak at 315 cm -1, corresponding to the A1 g vibrational mode associated with Sn-S bonds along the c-axis of the structure. Employing X ray Photoelectron Spectroscopy (XPS), the presence of essential components - Sn, S, and Pr - within the fabricated thin films was confirmed, consistent with experimental values of undoped and Pr -doped SnS2-x compositions. Importantly, the XPS analysis confirmed the integration of the Pr3+ oxidation state within Pr -doped SnS2 films. The photocatalytic degradation and antibacterial activities of the films were investigated. Notably, the photocatalytic potential of the synthesized materials against Congo Red exhibited a direct correlation with the Pr3+ doping percentage, indicating enhanced pollutant degradation with increasing doping levels. Similarly, the antibacterial performance against Escherichia coli displayed improvement with increasing Pr -doping content, highlighting the promising antimicrobial capabilities of the films. This study presents an innovative avenue to address both organic pollutant degradation and microbial control. By harnessing the attributes of Pr -doped SnS2 thin films, this research introduces a promising strategy for sustainable material applications in environmental purification and improvement in public health.
Citation - WoS: 122
Citation - Scopus: 126
CaXH₃ (X = Mn, Fe, Co) perovskite-type hydrides for hydrogen storage applications
(Wiley, 2020) Surucu, Gokhan; Gencer, Aysenur; Candan, Abdullah; Gullu, Hasan H.; Isik, Mehmet; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Hydrogen storage is one of the attractive research interests in recent years due to the advantages of hydrogen to be used as energy source. The studies on hydrogen storage applications focus mainly on investigation of hydrogen storage capabilities of newly introduced compounds. The present paper aims at characterization of CaXH3 (X: Mn, Fe, or Co) perovskite-type hydrides for the first time to understand their potential contribution to the hydrogen storage applications. CaXH3 compounds have been investigated by density functional theory studies to reveal their various characteristics and hydrogen storage properties. CaXH3 compounds have been optimized in cubic crystal structure and the lattice constants of studied compounds have been obtained as 3.60, 3.50, and 3.48 angstrom for X: Mn, Fe, and Co compounds, respectively. The optimized structures have negative formation enthalpies pointing out that studied compounds are thermodynamically stable and could be synthesized experimentally. The gravimetric hydrogen storage densities of X: Mn, Fe, and Co compounds were found in as 3.09, 3.06, and 2.97 wt%, respectively. The revealed values for hydrogen storage densities indicate that CaXH3 compounds may be potential candidates for hydrogen storage applications. Moreover, various mechanical parameters of interest compounds like elastic constants, bulk modulus, and Poisson's ratio have been reported throughout the study. These compounds were found mechanically stable with satisfying Born stability criteria. Further analyses based on Cauchy pressure and Pugh criterion, showed that they have brittleness nature and relatively hard materials. In addition, the electronic characteristics, band structures, and associated partial density of states of CaXH3 hydrides have been revealed. The dynamic stability behavior of them was verified based on the phonon dispersion curves.
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; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
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: 27
Citation - Scopus: 29
Composition-tuned band gap energy and refractive index in GaS_xSe_1-x layered mixed crystals
(Elsevier Science Sa, 2017) Isik, Mehmet; Gasanly, Nizami; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Transmission and reflection measurements on GaSxSe1-x mixed crystals (0 <= x <= 1) were carried out in the 400-1000 nm spectral range. Band gap energies of the studied crystals were obtained using the derivative spectra of transmittance and reflectance. The compositional dependence of band gap energy revealed that as sulfur (selenium) composition is increased (decreased) in the mixed crystals, band gap energy increases quadratically from 1.99 eV (GaSe) to 2.55 eV (GaS). Spectral dependencies of refractive indices of the mixed crystals were plotted using the reflectance spectra. It was observed that refractive index decreases nearly in a linear behavior with increasing band gap energy for GaSxSe1-x mixed crystals. Moreover, the composition ratio of the mixed crystals was obtained from the energy dispersive spectroscopy measurements. The atomic compositions of the studied crystals are well-matched with composition x increasing from 0 to 1 by intervals of 0.25. (C) 2016 Elsevier B.V. All rights reserved.
Citation - WoS: 10
Citation - Scopus: 10
Ellipsometric Study of Optical Properties of Gas_xse_{1-x< Layered Mixed Crystals}
(Elsevier Science Bv, 2016) Isik, Mehmet; Gasanly, Nizami; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Spectroscopic ellipsometry measurements were performed on GaSxSe1-x mixed crystals (0 <= x <= 1) in the 1.2-6.2 eV range. Spectral dependence of optical parameters; real and imaginary components of pseudodielectric function, pseudorefractive index and pseudoextinction coefficient were reported in the present work. Critical point (CP) analyses on second-energy derivative spectra of the pseudodielectric function were accomplished to find the interband transition energies. The revealed energy values were associated with each other taking into account the fact that band gap energy of mixed crystals rises with increase in sulfur content. The variation of CP energies with composition (x) was also plotted. Peaks in the spectra of studied optical parameters and CP energy values were observed to be shifted to higher energy values as sulfur concentration is increased in the mixed crystals. (C) 2016 Elsevier B.V. All rights reserved.
Citation - WoS: 10
Citation - Scopus: 10
Ellipsometry Study of Optical Parameters of Agin₅s_{8< Crystals}
(Elsevier, 2015) Isik, Mehmet; Gasanly, Nizami; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Agln(5)S(8) crystals grown by Bridgman method were characterized for optical properties by ellipsometry measurements. Spectral dependence of optical parameters; real and imaginary parts of the pseudodielectric function, pseudorefractive index, pseudoextinction coefficient, reflectivity and absorption coefficient were obtained from ellipsometiy experiments carried out in the 1.2-6.2 eV range. Direct band gap energy of 1.84 eV was found from the analysis of absorption coefficient vs. photon energy. The oscillator energy, dispersion energy and zero-frequency refractive index, high-frequency dielectric constant values were found from the analysis of the experimental data using Wemple-DiDomenico and Spitzer-Fan models. Crystal structure and atomic composition ratio of the constituent elements in the AgIn5S8 crystal were revealed from structural characterization techniques of X-ray diffraction and energy dispersive spectroscopy. (C) 2015 Elsevier B.V. All rights reserved
Citation - WoS: 11
Citation - Scopus: 12
Excitation Wavelength Dependent Nonlinear Absorption Mechanisms and Optical Limiting Properties of Bi12sio20 Single Crystal
(Elsevier, 2023) Dogan, Anil; Karatay, Ahmet; Isik, Mehmet; Pepe, Yasemin; Gasanly, Nizami; Elmali, Ayhan; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Nonlinear absorption mechanisms (NA), excitation wavelength dependence, and defect states of Bi12SiO20 (BSO) single crystal were investigated. The band gap and Urbach energies were found to be 2.51 and 0.4 eV from the absorption spectra. To evaluate the effect of excitation energy on the NA mechanism of the BSO single crystal, open aperture Z-scan experiment with 4 ns laser pulse at 532 and 1064 nm wavelengths with different intensities was performed. Obtained data were analyzed with a theoretical model considering the contributions of one photon absorption (OPA), two photon absorption (TPA) and free carrier absorption (FCA) to NA. The results indicated that the NA behavior decreased with increasing of the pump intensity as the defect states at around 2.32 eV by OPA at 532 nm, and TPA at 1064 nm excitations. The dominant NA mechanisms are OPA and sequential TPA at 532 nm as compared to the 1064 nm. A higher NA coefficient was obtained at 532 nm as compared to 1064 nm excitation. This observation was attributed to higher contribution of OPA at 532 nm even at lower input intensities compared to TPA contribution at 1064 nm. Onset optical limiting thresholds were found as 0.34 and 0.68 mJ/cm2 for 532 and 1064 nm input beams, respectively. In the light of the results, the BSO single crystal may be used as a saturable absorber or an optical limiter at convenient input intensity by effectively adjusting defect states and excitation wavelength.
Citation - WoS: 8
Citation - Scopus: 9
Experimental and Theoretical Investigation of the Mechanical Characteristics of Sillenite Compound: Bi₁₂geo_20<
(Elsevier Science Sa, 2021) Surucu, Gokhan; Isik, Mehmet; Gencer, Aysenur; Gasanly, Nizami; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
The present study reports the mechanical and elastic characteristics of Bi12GeO20 (BGO) compound by experimental nanoindentation measurements and density functional theory (DFT) calculations. X-ray diffraction pattern of BGO was plotted and revealed diffraction peaks were associated with Miller indices of cubic crystalline structure with lattice constant of a = 10.304 angstrom. Two- and three-dimensional representations of Young's modulus, linear compressibility, shear modulus and Poisson's ratio were presented according to DFT calculations. The calculated elastic constants pointed out the mechanically stable and anisotropic behavior of the BGO. The hardness and Young's modulus ranges of the BGO calculated from DFT studies were found as 3.7-6.3 GPa and 61.7-98.9 GPa, respectively. Hardness and Young's modulus of BGO single crystal were also obtained by analyzing force-dependent nanoindentation experimental data. It was observed that hardness and Young's modulus decrease with increase of load in the low applied loads and then reaches saturation in the high applied loads. This behavior is known as indentation size effect. True hardness value was determined from proportional specimen resistance model as 4.1 GPa. The force independent region presented the Young's modulus as 114 GPa. (C) 2021 Elsevier B.V. All rights reserved.
Citation - WoS: 1
Citation - Scopus: 1
Exploring the Thermal Stability of Sb2se3 for Potential Applications Through Advanced Thermal Analysis Methods
(Amer Chemical Soc, 2025) Altuntas, Gozde; Isik, Mehmet; Surucu, Gokhan; Parlak, Mehmet; Surucu, Ozge; Department of Electrical & Electronics Engineering; Electrical-Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 06. School Of Engineering; 01. Atılım University
Antimony selenide (Sb2Se3) is a promising material for energy applications, including photovoltaics, thermoelectrics, and photodetectors, due to its favorable electronic properties, availability, and low toxicity. However, its thermal stability, crucial for device efficiency and reliability, has been less explored, leaving a gap in understanding its high-temperature suitability. This study evaluates the thermal stability of Sb2Se3 using thermogravimetric analysis (TGA), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). The results show that Sb2Se3 remains stable up to 500 degrees C, with two significant weight loss stages: 1.75% between 500 and 610 degrees C, and 3.50% between 610 and 775 degrees C, indicating decomposition processes. Activation energies for the decomposition phases were determined as 121.8 and 57.2 kJ/mol using the Coats-Redfern method. Additionally, an endothermic phase transition was observed between 599 and 630.6 degrees C via DSC analysis. These findings demonstrate Sb2Se3's potential for high-temperature energy applications, providing essential insights for optimizing its use in solar cells, thermoelectric devices, and other technologies.
Citation - WoS: 129
Citation - Scopus: 133
First-Principle Investigation for the Hydrogen Storage Properties of Naxh₃ (x= Mn, Fe, Co) Perovskite Type Hydrides
(Pergamon-elsevier Science Ltd, 2019) Surucu, Gokhan; Candan, Abdullah; Gencer, Aysenur; Isik, Mehmet; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
In the present study, NaXH3 (X = Mn, Fe, Co) perovskite type hydrides have been investigated by performing first-principles calculation. The results of the structural optimizations show that all these compounds have negative formation energy implying the thermodynamic stability and synthesisability. The mechanical stability of these compounds has been studied with the elastic constants. Moreover, the polycrystalline properties like bulk modulus, Poisson's ratio, etc. have been obtained using calculated elastic constants of interest compounds. The electronic properties have been studied and band structures have been drawn with the corresponding partial density of states. These plots indicated that NaXH3 hydrides show metallic characteristics. The charge transfer characteristics in these compounds have been studied with the Bader partial charge analysis. The phonon dispersion curves and corresponding density of states indicated that NaXH3 compounds are dynamically stable compounds. The investigation on hydrogen storage characteristics of NaXH3 compounds resulted in hydrogen storage capacities of 3.74, 3.70 and 3.57 wt% for X = Mn, Fe and Co, respectively. The present study is the first investigation of NaXH3 perovskite type hydrides as known up to date and may provide remarkable contribution to the future researches in hydrogen storage applications. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 8
Citation - Scopus: 8
The Investigation of Electronic Nature and Mechanical Properties Under Spin Effects for New Half-Metallic Ferromagnetic Chalcogenides Ag₃crx_{4< (x = S, Se, and Te)}
(Elsevier, 2021) Erkisi, Aytac; Yildiz, Bugra; Wang, Xiaotian; Isik, Mehmet; Ozcan, Yusuf; Surucu, Gokhan; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
This study presents the electronic and mechanical characteristics of ternary silver-based Ag3CrX4 (X = S, Se, and Te) chalcogenides having simple cubic crystalline structure (SC), conforming P4-3m (space group: 215) that are studied under the spin-polarized Generalized Gradient Approach (GGA) within the framework of the Density Functional Theory (DFT). The stable magnetic phase has been determined as the ferromagnetic (FM) phase for all studied systems. Then, phase stability, mechanical, thermal and electronic characteristics of Ag3CrX4 chalcogenides have been reported. In the calculated spin polarized electronic band structures for Ag3CrX4 chalcogenides, as an indicator of half-metallic behavior, metallicity has been observed in the majority spin channel, while indirect band gaps (1.04 eV for Ag3CrS4, 1.10 eV for Ag3CrSe4, and 1.25 eV for Ag3CrTe4) have been determined in the minority spin channel. Moreover, Ag3CrX4 chalcogenides have been found as thermodynamically stable and structurally synthesizable considering the calculated negative formation enthalpies. Elastic constants of studied chalcogenides satisfying Born-Huang criteria's pointed out the mechanical stability of materials. The predicted mechanical properties determined with elastic constants revealed that Ag3CrX4 chalcogenides belong to soft and ductile material family.
Citation - WoS: 45
Citation - Scopus: 43
Investigation of Structural, Electronic, Magnetic and Lattice Dynamical Properties for Xcobi (x: Ti, Zr, Hf) Half-Heusler Compounds
(Elsevier, 2020) Surucu, Gokhan; Isik, Mehmet; Candan, Abdullah; Wang, Xiaotian; Gullu, Hasan Huseyin; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Structural, electronic, magnetic, mechanical and lattice dynamical properties of XCoBi (X: Ti, Zr, Hf) Half-Heusler compounds have been investigated according to density functional theory and generalized gradient approximation. Among alpha, beta and gamma structural phases, gamma-phase structure has been found as the most stability characteristics depending on the calculated formation enthalpies, energy-volume dependencies and Cauchy pressures. Energy-volume plots of possible magnetic orders of gamma-phase XCoBi compounds have been analyzed and the most stable order has been found as paramagnetic nature. The theoretical studies on gamma-phase structures resulted in band gap energies of 0.96, 0.99 and 0.98 eV for TiCoBi, ZrCoBi and HfCoBi semiconducting compounds, respectively. Born-Huang criteria applied on elastic constants of interest compounds has indicated that gamma-phase is also mechanically stable for all studied compounds. In addition, various mechanical, lattice dynamical and thermodynamical parameters of XCoBi compounds have been calculated in the present study.
Citation - WoS: 10
Citation - Scopus: 10
Low Temperature Thermoluminescence of Gd₂o_{3< Nanoparticles Using Various Heating Rate and t_{max< - t_{exc< Methods}}}
(Elsevier, 2019) Delice, Serdar; Isik, Mehmet; Gasanly, Nizami M.; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Thermoluminescence (FL) measurements for Gd2O3 nanoparticles were carried out for various heating rates between 0.3 and 0.8 K/s at low temperatures (10-280 K). TL spectrum exhibited two observable and one faint peaks in the temperature region of 10-100 K, and four peaks in the temperature region of 160-280 K. Heating rate analysis was achieved to understand the behaviors of trap levels. It was seen that the peak maximum temperatures and TL intensities of all peaks increase with increasing heating rate. This behavior was ascribed to anomalous heating rate effect. T-max - T(exc )analysis was accomplished for TL, peaks at relatively higher temperature region to reveal the related traps depths. T-max - T-exc plot presented a staircase structure indicating that the TL glow curve is composed of well separated glow peaks. Mean activation energies of trapping centers corresponding to these separated peaks were found as 0.43, 0.50, 0.58 and 0.80 eV.
Citation - WoS: 20
Citation - Scopus: 20
Nonlinear Optical Absorption Characteristics of Pbmoo₄ Single Crystal for Optical Limiter Applications
(Elsevier, 2022) Pepe, Yasemin; Isik, Mehmet; Karatay, Ahmet; Gasanly, Nizami; Elmali, Ayhan; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Molybdate materials take great interest due to their photocatalytic and optoelectronic applications. In this report, PbMoO4 single crystal, one of the member of molybdate materials, is grown by Czochralski technique and the change of nonlinear absorption characteristic depending on the input intensity was reported. Linear absorption analysis revealed the band gap energy and Urbach energy as to be 3.12 and 0.52 eV, respectively. Nonlinear absorption characteristics of the PbMoO4 single crystal was examined with the open aperture (OA) Z-scan experiments at 532 nm excitation wavelength under various input intensities. Fitting results of the OA Z-scan experiments indicated that PbMoO4 single crystal has nonlinear absorption (NA) behavior, and NA coefficient (beta(eff)) increased from 7.11 x 10(-8) to 1.96 x 10(-7) m/W with increasing input intensity. This observation was associated with the increase of the contribution of the free carrier absorption to the NA with the generation of more excited electrons with increasing input intensity. At the 532 nm excitation wavelength (2.32 eV), the dominant mechanisms were revealed as one photon and free carrier absorptions. The optical limiting threshold of the PbMoO4 single crystal was obtained to be 4.91 mJ/cm(2). The reported results indicated that PbMoO4 single crystal can be a good optical limiter in the visible wavelength region due to its effective NA behavior.
Citation - WoS: 2
Citation - Scopus: 3
Optical and Nanomechanical Properties of Ga₂se_{3< Crystals and Thin Films}
(Springer, 2021) Isik, Mehmet; Emir, Cansu; Gullu, Hasan Huseyin; Gasanly, Nizami; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
The optical and nanomechanical properties of Ga(2)Se(3)single crystals and thin films were investigated using reflection, transmission, and nanoindentation measurements. The reflection spectrum recorded in the 525- to 1100-nm range was analyzed to get the band gap energy of the crystal structure, and derivative analysis of the spectrum resulted in band gap energy of 1.92 eV which was attributed to indirect transition. The band gap energy of thermally evaporated Ga(2)Se(3)thin film was determined from the analysis of the transmittance spectrum. The absorption coefficient analysis presented the direct band gap energy as 2.60 eV. The refractive index was investigated in the transparent region using the Wemple-DiDomenico single-oscillator model. Nanoindentation measurements were carried out on the crystal and thin film structures of Ga2Se3. Nanohardness and elastic modulus of the Ga(2)Se(3)single crystals and thin films were calculated following the Oliver-Pharr analysis method.
Citation - WoS: 5
Citation - Scopus: 5
Optical Characterization of Cuin₅s_{8< Crystals by Ellipsometry Measurements}
(Pergamon-elsevier Science Ltd, 2016) Isik, Mehmet; Gasanly, Nizami; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Optical properties of CuIn5S8 crystals grown by Bridgman method were investigated by ellipsometry measurements. Spectral dependence of optical parameters; real and imaginary parts of the pseudodielectric function, pseudorefractive index, pseudoextinction coefficient, reflectivity and absorption coefficients were obtained from the analysis of ellipsometry experiments performed in the 1.2-6.2 eV spectral region. Analysis of spectral dependence of the absorption coefficient revealed the existence of direct band gap transitions with energy 1.53 eV. Wemple-DiDomenico and Spitzer-Fan models were used to find the oscillator energy, dispersion energy, zero-frequency refractive index and high-frequency dielectric constant values. Structural properties of the CuIn5S8 crystals were investigated using X-ray diffraction and energy dispersive spectroscopy analysis. (C) 2015 Elsevier Ltd. All rights reserved.
Citation - WoS: 4
Citation - Scopus: 4
Optical Characterization of Ga₂ses Layered Crystals by Transmission, Reflection and Ellipsometry
(World Scientific Publ Co Pte Ltd, 2015) Isik, Mehmet; Gasanly, Nizami; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Optical 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.
Citation - WoS: 7
Citation - Scopus: 7
Optical Properties of Gas Crystals: Combined Study of Temperature-Dependent Band Gap Energy and Oscillator Parameters
(Natl inst Science Communication-niscair, 2017) Isik, Mehmet; Tugay, Evrin; Gasanly, Nizami; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics Engineering; 15. Graduate School of Natural and Applied Sciences; 01. Atılım University
Optical parameters of gallium sulfide (GaS) layered single crystals have been found through temperature-dependent transmission and room temperature reflection experiments in the wavelength range of 400-1100 nm. Experimental data demonstrates the coexistence of both optical indirect and direct transitions and the shift of the absorption edges toward lower energies by increasing temperature in the range of 10-300 K. Band gap at zero temperature, average phonon energy and electron phonon coupling parameter for indirect and direct band gap energies have been obtained from the analyses of temperature dependences of band gap energies. At high temperatures kT>> (E-ph), rates of band gap energy change have been found as 0.56 and 0.67 me V/K for E-gi and E-gd, respectively. Furthermore, the dispersion of refractive index has been discussed in terms of the Wemple-DiDomenico single effective oscillator model. The refractive index dispersion parameters, namely oscillator and dispersion energies, oscillator strength and zero-frequency refractive index, have been found to be 4.48 eV, 24.8 eV, 6.99x10(13) m(-2) and 2.56, respectively. The results of the present work will provide an important contribution to the research areas related to the characterization and optoelectronic device fabrication using GaS layered crystals.