Browsing by Author "Gullu, Hasan Huseyin"

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Citation - WoS: 1
Deposition and Characterization of ZnSnSe₂ Thin-Films Deposited by Using Sintered Stoichiometric Powder
(Gazi Univ, 2019) Bayrakli Surucu, Ozge; Gullu, Hasan Huseyin
In this work, ZnSnSe2 (ZTSe) thin films were deposited using crystalline powder grown by vertical Bridgman-Stockbarger technique. The deposition process was carried out by means of e-beam evaporation on the well-cleaned soda lime glass substrates and keeping them at the substrate temperature of 200 degrees C. The structural, optical and electrical properties of ternary ZTSe thin films were investigated depending on the annealing temperature at 250 and 300 degrees C. X-ray diffraction analysis showed that as-grown films were in amorphous structure, however annealing at 250 degrees C triggered the crystallization on the preferred ternary structure and annealing at 300 degrees C resulted in the changes from amorphous to the polycrystalline structure. Using the compositional analysis, the detail information about the stoichiometry and the segregation mechanisms of the constituent elements in the structure were determined for both as-grown and annealed samples. In addition, they were morphologically characterized using scanning electron microscopy technique. The electrical properties were analyzed using temperature dependent dark- and photo-conductivity measurements. From the variation of electrical conductivity as a function of the ambient temperature, the current transport mechanisms and corresponding activation energies at specific temperature intervals for each sample were determined. The optical properties for the ZTSe thin films were studied depending on the structural changes with annealing.
Citation - WoS: 23
Citation - Scopus: 24
First Principles Study on the Structural, Electronic, Mechanical and Lattice Dynamical Properties of Xrhsb (x = Ti and Zr) Paramagnet Half-Heusler Antimonides
(Iop Publishing Ltd, 2019) Surucu, Gokhan; Candan, Abdullah; Erkisi, Aytac; Gencer, Aysenur; Gullu, Hasan Huseyin
The half-Heusler TiRhSb and ZrRhSb alloys in the formation of face-centered cubic MgAgAs-type structure, which conforms to the F (4) over bar 3m space group with 216 as the space number, have been investigated using Generalized Gradient Approximation (GGA) implemented in Density Functional Theory (DFT). The calculated formation enthalpies and the plotted energy-volume curves of different types of structural phases (alpha, beta, and gamma) in these alloys indicate that the gamma-phase structure is the best energetically suitable structure. In addition, TiRhSb and ZrRhSb alloys have been found as paramagnetic (PM) with the investigation of antiferromagnetic (AFM), ferromagnetic (FM), and paramagnetic (PM) orders in the most stable gamma-phase structure. Therefore, their electronic, mechanical, and dynamical properties have been examined in the gamma structural phase and paramagnetic order. These alloys have semiconducting nature due to the observed same band gaps in both the majority and minority spin channels of the calculated spin-polarised electronic band structure. These calculated band gaps are 0.75 eV for gamma-TiRhSb and 1.18 eV for gamma-ZrRhSb. The predicted elastic constants indicate that the alloys in this study are mechanically stable and show nearly isotropic behavior in the gamma structural phase. Also, the minimum and the diffuson thermal conductivites have been determined for these alloys. Finally, the calculated phonon dispersion spectras for the gamma-TiRhSb and gamma-ZrRhSb half-Heusler antimonide alloys show the dynamic stability of these systems.
Citation - WoS: 8
Citation - Scopus: 9
First-principles studies of Tin+1SiN_n (n=1, 2, 3) MAX phase
(Taylor & Francis Ltd, 2020) Surucu, Gokhan; Gullu, Hasan Huseyin; Candan, Abdullah; Yildiz, Bugra; Erkisi, Aytac
In this study, the structural, electronic, mechanical, lattice dynamical and thermodynamic characteristics of ( 1, 2 and 3) phase compounds were investigated using the first principle calculations. These ternary nitride compounds were found to be stable and synthesisable, and the results on the stability nature of them were also evaluated for the possible and phases. -was found to be the most stable one among these new class of layered phases for which limited works are available in the literature. The band structures, that are essential for the electronic properties, were determined along with the partial density of states (PDOS) indicating the metallic behaviour of these compounds. The polycrystalline elastic moduli were calculated based on the single-crystal elastic constants and the mechanical stabilities were verified. Some basic physical parameters, such as bulk modulus, shear modulus, Young's modulus, Poisson's ratio, Debye temperature, and sound velocities, were also predicted. Furthermore, the anisotropic elastic properties were visualised in three dimensions (3D) for Young's modulus, linear compressibility, shear modulus and Poisson's ratio as well as with the calculation of the anisotropic factors. - phase showed the most isotropic characteristics with minimum deviations. These theoretical values were also used to identify the stiffness and ionic characteristics. The phonon dispersion curves and corresponding PDOS indicated that compounds were dynamically stable. Moreover, thermodynamic properties obtained from phonon dispersion curves were investigated in detail.
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
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: 3
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
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: 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.