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Citation - WoS: 29
Citation - Scopus: 31
Composition-tuned band gap energy and refractive index in GaS_xSe_1-x layered mixed crystals
(Elsevier Science Sa, 2017) Isik, Mehmet; Gasanly, Nizami
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: 9
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
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: 10
Citation - Scopus: 15
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
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: 47
Citation - Scopus: 44
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
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: 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: 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: 23
Citation - Scopus: 22
Wavelength Dependence of the Nonlinear Absorption Performance and Optical Limiting in Bi12tio20 Single Crystal
(Elsevier, 2023) Pepe, Yasemin; Isik, Mehmet; Karatay, Ahmet; Gasanly, Nizami; Elmali, Ayhan
In this study, the influence of excitation wavelength and input intensity on the nonlinear absorption (NA) mechanism and optical limiting behavior of the Bi12TiO20 (BTO) single crystal were reported. The energy band gap of the BTO single crystal was obtained to be 2.38 eV. Urbach energy revealed that the single crystal has a highly defective structure. Open aperture (OA) Z-scan experiments were conducted at 532 and 1064 nm exci-tation wavelengths at various input intensities. Obtained experimental data were analyzed with a theoretical model considering one photon, two-photon and free carrier absorption contributions to NA. The obtained results revealed that the BTO single crystal possesses NA. The NA coefficient increased with increasing input intensity at 532 nm excitation wavelength, while it decreased with increasing input intensity at 1064 nm excitation wave-length. Due to the intense localized defect states distribution at the energy of 532 nm excitation wavelength within the band gap, increasing contribution to NA came from one photon absorption (OPA), sequential two -photon absorption (TPA) and free carrier absorption (FCA) with increasing input intensity. The filling of the defect states at 1064 excitation wavelength caused a reduction in NA due to increasing saturable absorption with increasing input intensity. TPA coefficients were also found from the fitting ignoring the defect states. As ex-pected, the values of the nonlinear absorption coefficient beta eff are higher than that of the TPA coefficients for both excitation wavelengths. The optical limiting threshold of the BTO single crystal was obtained to be 6.62 mJ/cm2. The results of the present works indicated that BTO single crystal can be used as a potential optical limiter.
Citation - WoS: 21
Citation - Scopus: 21
The Role of Defects on the Transition From Saturable Absorption To Nonlinear Absorption of Bi₁₂geo_{20< Single Crystal Under Increasing Laser Excitation}
(Elsevier, 2022) Pepe, Yasemin; Isik, Mehmet; Karatay, Ahmet; Yildiz, Elif Akhuseyin; Gasanly, Nizami; Elmali, Ayhan
This work reports defect and input intensity dependent nonlinear optical behaviors of Bi12GeO20 (BGO) single crystal. Open aperture (OA) Z-scan experiments were performed with 532 nm excitation wavelength under 4 ns and 100 fs pulsed laser irradiation. Obtained data were fitted with a theoretical model considering one-photon, two-photon and free carrier absorption contributions to nonlinear absorption due to longer lifetime of localized defect states than that of used laser pulse durations. At low input intensities, the BGO single crystal showed saturable absorption (SA) behavior and transition to nonlinear absorption (NA) behavior observed with further increase of the input intensities both of pulse durations. At low input intensity, the OPA mechanism is dominant and results in SA by filling of the defect states due to defect state at around one photon energy (2.32 eV). At higher input intensity, multi-photon, two-photon and free carrier absorption become dominant mechanisms, and nonlinear absorption behavior was observed. The lowest saturation threshold was found as 1.36 x 1010 W/cm2 with nanosecond pulses. We have revealed the mechanisms contributing both SA and NA, and determined saturation intensity threshold and effective nonlinear absorption coefficients. Our findings indicate that the tails of defect states overlap in the energy band gaps especially in sufficiently disordered crystal. With this way, the spectral range for saturable absorption and nonlinear absorption can be broadened.
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
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: 2
Citation - Scopus: 2
Temperature-Tuned Band Gap Energy and Oscillator Parameters of Gas_0.5se_{0.5< Single Crystals}
(Elsevier Gmbh, Urban & Fischer verlag, 2016) Isik, Mehmet; Tugay, Evrin; Gasanly, Nizami
Temperature-dependent transmission and room temperature reflection measurements were carried out on GaS0.5Se0.5 single crystal in the wavelength range of 380-1000 nm to investigate its optical parameters. The analysis of the temperature-dependent absorption data showed that direct and indirect band gap energies increase from 2.36 to 2.50 eV and 2.27 to 2.40 eV, respectively, as temperature is decreased from 300 to 10 K. The rates of change of the direct and indirect band gap energies with temperature was found around -7.4 x 10(-4) eV/K from the analysis of experimental data under the light of theoretical relation giving the band gap energy as a function of temperature. The absolute zero value of the band gap energies were also found from the same analysis as 2.50 eV (for direct) and 2.40 eV (for indirect). Wemple-DiDomenico single effective oscillator model, Sellmeier oscillator model and Spitzer-Fan model were used for the room temperature reflection data to find optical parameters of the crystal. (C) 2016 Elsevier GmbH. All rights reserved.

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