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Öğe Comparing Different Approaches to Form Cobalt Oxide Layer on CoPt Nanoparticles(Adiyaman University, 2020) Kaya, Dogan; Adanur, Idris; Akyol, Mustafa; Karadag, Faruk; Ekicibil, AhmetWe have studied the effect of preparation methods, under argon gas and in the air environment, on the cobalt oxide formation of CoPt nanoparticles by the polyol process. The formation of cobalt oxide for both samples was investigated by the x-ray diffraction (XRD) method and cobalt oxide peaks are observed in the air prepared sample. Rietveld refinement analyses revealed that all samples exhibit a chemically distorted cubic crystal structure. The average particle size was determined <8 nm by scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) was revealed the chemical compositions with possible oxygen formation in the structure. The blocking temperature is reduced to 28 K in the air prepared sample due to cobalt oxide formation. The hysteresis gap disappeared above the blocking temperature and no saturation is observed up to ±5 T external field due to the system switching from ferromagnetic state to paramagnetic state. Similarly, the coercive field was decreased from 1021 Oe to zero with increasing the temperature from 5 K to 300 K. The formations of the cobalt oxide layer did not interact with CoPt nanoparticles, therefore, the maximum exchange bias was observed about 93 Oe at 5 K. © 2020, Adiyaman University. All rights reserved.Öğe Detailed investigation of structural and magnetic properties of multiphase binary Pd-Co alloys prepared by modified polyol process(Elsevier Science Sa, 2021) Kaya, Dogan; Adanur, Idris; Akyol, Mustafa; Karadag, Faruk; Ekicibil, AhmetPd-Co based magnetic alloy nanoparticles were prepared by the modified polyol process and stabilized by polyvinylpyrrolidone (PVP) and 3-aminopropyl-trimethoxysilane (APES) capping agents and further reduction of metal salts with Sodium borohydride (NaBH4) at high temperature to form desired NPs. We have a detailed investigation of the effect of Pd concentration in the Pd-Co alloy NPs on structural and magnetic properties. XRD and Rietveld refinement analyses were confirmed that the multiphase structures of fcc-PdCo, fcc-Co, and hcp-Co phases coexist at low Pd loading samples. Over %50 of Pd loading resulted in a single fcc-PdCo phase with reduced lattice parameter to 4.0079 angstrom and d((111))-space to 2.31 angstrom. TEM and SEM images reveal well dispersed and uniformly distributed NPs with an average particle sizes of below 7 nm. The elemental compositions and the characteristic OH, CH, CO stretching peaks of capping agents were confirmed by EDS and FT-IR spectrums, respectively. M(T) and M(H) curves revealed that there are multi magnetic phase transitions in the Pd-Co structure as a function of Pd loading from superparamagnetic to ferromagnetic phase or back to superparamagnetic phase by reducing the temperature from 300 K to 5 K. We observed that the blocking temperature (T-B) could not be detected due to 5% Pd loading below 300 K, while it reduced up to 55 K at high Pd loading of 62%. The coercive field (H-c) was increased to similar to 1900 Oe for Pd0.62Co0.38 sample due to the smallest particle size as 5.26 nm. The highest amount of Co resulted in maximum saturation magnetization (M-s) up to 65.5 emu/g for 5% Pd concentration. We measured the M-r/M-s ratios were less than 0.5, which is due to the internal stress that results in the uniaxial magnetic anisotropy in the structure. The maximum K-eff and mu(f.u). values were found to be over 12.9 x 10(6) erg/cm(3) and 0.72 mu(B) at 5 K for 5% Pd concentration, respectively. (C) 2021 Elsevier B.V. All rights reserved.Öğe Investigating the optical, electronic, magnetic properties and DFT of NiO films prepared using RF sputtering with various argon pressures(Elsevier, 2023) Hopoglu, Hicret; Kaya, Dogan; Maslov, Mikhail M.; Kaya, Savas; Demir, Lkay; Altuntas, Ismail; Ungan, FatihIn this study, we investigated the structural, optical, magnetic, and conductive properties of nickel oxide (NiO) films on glass substrates deposited using Radio Frequency (RF) magnetron sputtering with varying Ar gas pressure and thickness. X-ray diffraction and Rietveld refinement analysis confirmed a cubic crystal structure and showed that the lattice parameters and the d(111)-space increased from 4.0559 & ANGS; to 4.2712 & ANGS; and from 2.3208 & ANGS; to 2.4582 & ANGS;, respectively, due to increased Ar pressure during deposition. Scanning electron microscopy and atomic force microscopy were used to determine the cross-sectional and surface topology of the NiO films, which exhibited uniform and homogeneous growth with an average spherical size of 54.28 & PLUSMN; 0.33 nm. The optical bandgap values of the films were calculated to be between 3.26 and 3.65 eV, increasing with pressure. Hall measurements confirmed the p-type semiconductor nature of the films with an average sheet carrier density of 1010 cm ? 2. The films exhibited soft magnetic properties, with a maximum Hc and Ms of 178.5 Oe and 5.82 emu/ cm3 for 246 nm NiO film, respectively. Density functional theory (DFT) calculations confirmed the experimental results for both single to five layers NiO films and bulk NiO formations. The refined energy gap value was found to be 3.2 eV by the DFT calculation. The films produced at room temperature were found to be stable and reproducible, making them suitable as p-type materials for device construction.Öğe Investigation of Magnetic Anisotropy in the Ni-Ge and Ni(NiO)-Ge Thin Films(Elsevier, 2021) Kaya, Dogan; Akyol, Mustafa; Wang, Yitao; Guo, Quanmin; Karadag, Faruk; Ekicibil, AhmetWe studied the structural and magnetic properties of Ni-Ge and Ni(NiO)-Ge films deposited by physical vapor deposition technique on the Si/SiO2 substrate. The x-ray diffraction (XRD) analysis show that as-prepared samples exhibit clear peaks of Ge, Ni, and Au with a cubic symmetry belongs to space group Fm (3) over barm. Due to the thermal annealing process at 350 degrees C, NiO layer formed on Ni layer. The NiO formation has reduced the interaction of Ni-Ge interlayer which is confirmed by XRD data. Investigation of temperature-dependent magnetic moment revealed the Neel and the critical temperatures as 93 and 294 K, respectively. The hysteresis loops showed that the preferred magnetization direction for samples at 300 K is the in-plane (parallel) which reaches saturation easier than out-of-plane (perpendicular) loops. The formation of NiGe interlayer resulted in a magnetically dead-region which led to decrease ferromagnetic domain and the coercive field. (C) 2020 Elsevier B.V. All rights reserved.Öğe Magnetic and optical properties of ZnO/Ni/ZnO multilayer film on Si(100) and sapphire substrates(Elsevier Gmbh, 2022) Kaya, Dogan; Akyol, Mustafa; Tuzemen, Ebru Senadim; Ekicibil, AhmetThe optical absorption, band gap, and magnetic properties of ZnO/Ni(t)/ZnO multilayer film structures were investigated in various Ni layer thicknesses and substrates. We deposited 1, 4, and 5 nm of Ni film by thermal evaporation technique that sandwiched between ZnO films (similar to 15 nm) via radio frequency magnetron sputtering method on both Si(100) and sapphire substrates. Although x-ray diffraction (XRD) analysis confirmed the (002) crystalline plane of ZnO without any Ni crystal phases on Si(100) surface, the better crystalline directions of ZnO, hexagonal wurtzite structure, was observed on the sapphire substrate. In the XRD analysis, we observed the cubic structure of NiO film formation due to thermally oxidation of Ni ions with interactions ZnO layer. Atomic force microscopy images confirmed the effect of the Ni layer on the average island size of 23.9 +/- 2.9 nm and 25.6 +/- 6.2 of ZnO films on 4 and 5 nm Ni films, respectively. Energy dispersive x-ray spectroscopy data confirmed that there is no other atom or impurity in the sample structure. The optical transparency of the multilayer films was reduced with increasing Ni layer thickness and maximum transparency was obtained as 97% at 800 nm of wavelength for the film with 1 nm Ni. The direct optical band gap of ZnO/Ni(t)/ZnO films was found to be 3.25, 3.20, and 3.12 eV with the contribution of 1, 4, and 5 nm Ni film in the multilayer film stack. The maximum H-c is found to be 1000 Oe for Si substrates and this value is reduced to around 400 Oe due to the crystal formation of the NiO layer for sapphire substrate samples.Öğe Magnetically separable low Pt substituted Co nanoparticles: Investigation of structural, magnetic, and catalytic properties(Elsevier, 2022) Kaya, Dogan; Isik, Hasan Huseyin; Isik, Ilknur Baldan; Adanur, Idris; Wang, Yitao; Akyol, Mustafa; Karadag, FarukDeveloping multifunctional nanoparticles (NPs) for magnetic and catalytic purposes is crucial for controlling magnetic properties and reducing production costs. We synthesized Co and low Pt loaded CoPt NPs by the modified polyol process. Co and CoPt NPs exhibited coexist fcc and hcp phases which are confirmed with x-ray diffraction and Rietveld refinement analysis. Scanning electron microscopy images revealed the average size of the NPs smaller than 9 nm with a narrow distribution. An irreversible magnetization-temperature behavior of the particles is observed in the modes of zero-field cooled and field cooled with a strong ferromagnetic signal close to 350 K. The field-dependent magnetization up to +/- 5 T was investigated to determine coercive field (H-c), exchange bias (H-E), saturation magnetization (M-s), remanent magnetization (M-r), and the ratio of remanent magnetization to saturation magnetization (M-r/M-s). There is a general decrease in magnetic values due to an increase of both the temperature and the Pt ratio in Co nanoparticles. When the Pt/Co ratio drops to 1%, the sample was measured with the highest H-c value of 648.5 Oe and M-s value of 100 emu/g at 5 K. On the contrary, increasing the concentration of Pt to 10% resulted in a reduction for the M-s value below 40 emu/g. Besides, cyclic voltammetry measurements showed apparent hydrogen reduction in the potential range of -0.91 V and -0.96 V (vs Ag/AgCl) and 10% Pt loaded CoPt NPs exhibits the highest activity after 10th cycles and increase the activity up to 15.80 mA cm(-2) at -1.2 V due to the surfactant.Öğe Magnetically separable low Pt substituted Co nanoparticles: Investigation of structural, magnetic, and catalytic properties(Elsevier, 2022) Kaya, Dogan; Isik, Hasan Huseyin; Isik, Ilknur Baldan; Adanur, Idris; Wang, Yitao; Akyol, Mustafa; Karadag, FarukDeveloping multifunctional nanoparticles (NPs) for magnetic and catalytic purposes is crucial for controlling magnetic properties and reducing production costs. We synthesized Co and low Pt loaded CoPt NPs by the modified polyol process. Co and CoPt NPs exhibited coexist fcc and hcp phases which are confirmed with x-ray diffraction and Rietveld refinement analysis. Scanning electron microscopy images revealed the average size of the NPs smaller than 9 nm with a narrow distribution. An irreversible magnetization-temperature behavior of the particles is observed in the modes of zero-field cooled and field cooled with a strong ferromagnetic signal close to 350 K. The field-dependent magnetization up to +/- 5 T was investigated to determine coercive field (H-c), exchange bias (H-E), saturation magnetization (M-s), remanent magnetization (M-r), and the ratio of remanent magnetization to saturation magnetization (M-r/M-s). There is a general decrease in magnetic values due to an increase of both the temperature and the Pt ratio in Co nanoparticles. When the Pt/Co ratio drops to 1%, the sample was measured with the highest H-c value of 648.5 Oe and M-s value of 100 emu/g at 5 K. On the contrary, increasing the concentration of Pt to 10% resulted in a reduction for the M-s value below 40 emu/g. Besides, cyclic voltammetry measurements showed apparent hydrogen reduction in the potential range of -0.91 V and -0.96 V (vs Ag/AgCl) and 10% Pt loaded CoPt NPs exhibits the highest activity after 10th cycles and increase the activity up to 15.80 mA cm(-2) at -1.2 V due to the surfactant.Öğe Optical properties of NiO films: Effect of nitrogen-doping, substrate temperature and band gap estimation using machine learning(Elsevier Ltd, 2024) Kaya, Dogan; Hopoğlu, Hicret; Çelik, Ali; Akyol, Mustafa; Karadag, Faruk; Şenadım Tüzemen, Ebru; Ekicibil, AhmetIn this study, nickel oxide (NiO) thin films were synthesized on glass substrates using RF magnetron sputtering with varying nitrogen (N) doping ratio and substrate temperatures to explore modifications in their structural, morphological, and optical properties. The films were prepared using a high-purity NiO target under controlled sputtering conditions. Structural analysis by X-ray diffraction revealed an improvement in crystallinity in the (2 0 0) direction with increasing N ratio. In contrast, higher N ratio led to the suppression of (1 1 1) and (2 2 0) peaks, indicating a significant influence of N on the crystal structure and orientation. The films’ thickness and morphology, examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy, showed uniform and homogeneous growth with smooth surface topologies. Optical properties, assessed by UV–Vis-NIR spectrophotometry, demonstrated a decrease in transmittance and a redshift in the absorption edge with increased N doping, corresponding to a narrowing of the energy bandgap from 3.7 eV to 3.45 eV. This bandgap reduction is attributed to N incorporation substituting oxygen sites, introducing defect states within the band structure. Additionally, the impact of substrate temperature on film growth enhanced crystallinity and orientation along the (1 1 1) plane at higher temperatures, with a simultaneous reduction in film thickness due to increased adatom mobility and potential thermal decomposition. The evaluation of Kernel Ridge Regression (KRR) and Ridge Regression (RR) models revealed their effectiveness in predicting band gap values for thin films at varying substrate temperatures and thicknesses. While RR excelled in predicting a band gap of 3.6 eV for a film with a substrate temperature of 24 °C and a thickness of 112.7 nm, KRR outperformed in predicting a band gap of 3.65 eV for a film with a substrate temperature of 24 °C and a thickness of 107 nm. These findings elucidate the dual influence of N doping and substrate temperature on enhancing the functional properties of NiO thin films, promising for applications in optoelectronic devices and gas sensors. © 2024 Elsevier B.V.Öğe Self-Defined Transition State in Hybrid C70-Au Clusters Created by the Scanning Tunneling Microscope Tip(Amer Chemical Soc, 2019) Kaya, Dogan; Wang, Yitao; Akyol, Mustafa; Karadag, Faruk; Ekicibil, Ahmet; Guo, QuanminManipulation of C-70-Au hybrid nanoclusters was investigated using a scanning tunneling microscope (STM) tip. We demonstrate that removing a selected C-70 molecule from the cluster by STM-tip resulted in an intermediate transition state without thermal decomposition. The molecule rotates and diffuses around the cluster and leaves the cluster without taking an additional molecule and Au atoms due to the rather weak interaction between molecules and the surface atoms. After removing a C-70 molecule, the van der Waals interaction among the remaining C-70 molecules leads to reorganization of the cluster. This self-transition-state is due to a weak charge transfer between the molecules and the surface. The extraction of molecules in a Reshape Transition Interstate ring cluster resulted in polygonal Au island formation.Öğe Synthesis of monodisperse CoPt nanoparticles: Structural and magnetic properties(Elsevier, 2021) Kaya, Dogan; Adanur, Idris; Akyol, Mustafa; Karadag, Faruk; Ekicibil, AhmetWe have investigated CoPt nanoparticles by the simultaneous reduction of Pt (acac)(2) and Co (acac)(2) with polyol method under N-2 atmosphere. The formation of CoPt nanoparticles requires further study of possible increased Pt concentration and size effects on their structural and magnetic properties. We found that as-synthesized CoPt NPs exhibits a chemically disordered cubic phase in the compositions with an average crystalize size of 4.44 nm confirmed by X-ray diffraction (XRD) method and Rietveld refinement analyses. Uniformly distributed the average cluster size of CoPtx nanoparticles decreased from 13.7 nm to 7.6 nm with decreased Pt concentration from 2.3 to 0.5 which determined by scanning electron microscopy (SEM). Magnetic properties are characterized by vibrating sample magnetometer (VSM) for zero field cooled (ZFC) and field cooled (FC) conditions between 5 and 300 K and applied field up to +/- 5 T. Magnetic results indicate that the Co rich CoPtx nanoparticles exhibit large coercive field up to 1358 Oe at 5 K and this value decrease with increasing temperature and Pt concentration for all samples. Due to a transition from ferromagnetic to a superparamagnetic phase with elevated temperature, coercivity and exchange bias nearly vanished for all samples. (C) 2020 Elsevier B.V. All rights reserved.Öğe Synthesis of monodisperse CoPt nanoparticles: Structural and magnetic properties(Elsevier, 2021) Kaya, Dogan; Adanur, Idris; Akyol, Mustafa; Karadag, Faruk; Ekicibil, AhmetWe have investigated CoPt nanoparticles by the simultaneous reduction of Pt (acac)(2) and Co (acac)(2) with polyol method under N-2 atmosphere. The formation of CoPt nanoparticles requires further study of possible increased Pt concentration and size effects on their structural and magnetic properties. We found that as-synthesized CoPt NPs exhibits a chemically disordered cubic phase in the compositions with an average crystalize size of 4.44 nm confirmed by X-ray diffraction (XRD) method and Rietveld refinement analyses. Uniformly distributed the average cluster size of CoPtx nanoparticles decreased from 13.7 nm to 7.6 nm with decreased Pt concentration from 2.3 to 0.5 which determined by scanning electron microscopy (SEM). Magnetic properties are characterized by vibrating sample magnetometer (VSM) for zero field cooled (ZFC) and field cooled (FC) conditions between 5 and 300 K and applied field up to +/- 5 T. Magnetic results indicate that the Co rich CoPtx nanoparticles exhibit large coercive field up to 1358 Oe at 5 K and this value decrease with increasing temperature and Pt concentration for all samples. Due to a transition from ferromagnetic to a superparamagnetic phase with elevated temperature, coercivity and exchange bias nearly vanished for all samples. (C) 2020 Elsevier B.V. All rights reserved.
