Browsing by Author "Arda L."

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Correlation between crystal defects and room temperature ferromagnetism of hydrothermally grown Eu substituted ZnO nanorods
(2022-11-15) Kaya S.; Ozturk O.; Arda L.
The hydrothermal method has been used to grow zinc oxide nanorods on a glass substrate with different Europium (Eu) concentrations. The Eu doping effect on the structural, optical, and magnetic properties of the samples was systematically investigated. The undoped sample exhibited diamagnetic behaviour, while soft room temperature ferromagnetism was observed in all the Eu substituted samples. With regard to the hysteresis loops, the highest coercivity, saturated magnetic moment, and retentive magnetic moment values were observed to be 41.64 Oe, 18.86 × 10−6 emu, and 2.17 × 10−6 emu, respectively, for ZnO:Eu 7%. According to the relationships between the magnetic properties, Eu doping levels, and defects concentrations, it can be concluded that the room temperature ferromagnetism observed in the samples is caused by crystal point defects including oxygen vacancies and zinc interstitials, rather than carrier-mediated exchange interactions, which is also consistent with the bound magnetic polarons theory.
Effect of doping on microstructure and optical properties of ternary structure of Zn1−x−yBxCyO (B=Cu, C=Co) nano thin films
(2020-12-01) Asikuzun E.; Ozturk O.; Terzioglu R.; Arda L.; Terzioglu C.
We report the results of an in depth study of optical and microstuctural properties of thin films of Zn1−x−yCuxCoyO system (x = 0,00 and 0.02, y = 0.00, 0.01, 0.02, 0.03, 0.04. and 0.05) which are grown by the sol–gel method. We have performed differential thermal analysis, and thermo gravimetric analysis/difference thermogravimetric analysis, x-ray diffraction, scanning electron microscopy, energy dispersive spectrometer, atomic force microscopy and UV–VIS spectrophotometer experiments. We have found that all of the studied samples are in hexagonal wurtzite structure and oriented along the (002) direction with a very weak signal for the (101) reflection. We have also found that the lattice parameter c increases with doping. All the films showed wrinkle network structure with nano-sized crystals and the grain size was observed to decrease with increasing Co doping. The bandgap was found to decrease from 3.28 to 3.22 eV with doping. All the above results will be discussed in detail.
Enhanced mechanical properties of yttrium doped ZnO nanoparticles as determined by instrumented indentation technique
(2018-06-15) Kaya S.; Akcan D.; Ozturk O.; Arda L.
Yttrium doped (1, 3 and 5 wt%) zinc oxide nanoparticles were synthesized via sol-gel process. The phase, structural and mechanical properties were investigated using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and micro hardness based on indentation technique. The lattice parameters and grain sizes of the samples were calculated from the XRD data. As the lattice parameters increased, the grain sizes decreased dramatically, resulting in more grain boundaries and strong grain connectivity in the ZnO microstructure. Load-depth curves were obtained by applying indentation loads in the range from 400 to 2000 mN at room temperature. As the Y concentration increased, a significant increase was observed in the hardness values computed from loading-unloading curves using the Oliver and Pharr method. The indentation modulus of the samples reached a saturation value for 3% Y and then decreased as the doping rate increased. Moreover, the crack formation around the indent on the sample surface was examined by electron microscopy and was identified as radial/median type. The fracture toughness of the samples was calculated using the Vickers indentation fracture method. Increased fracture toughness values confirm that ZnO nanoparticles are mechanically strengthened by Y doping.
High-quality c-axis oriented non-vacuum Er doped ZnO thin films
(2016-05-15) Asikuzun E.; Ozturk O.; Arda L.; Tasci A.; Kartal F.; Terzioglu C.
Preparation, growth, structure and optical properties of high-quality c-axis oriented non-vacuum Er doped ZnO thin films were studied. Zn1-xErxO (x=0.0, 0.01, 0.02, 0.04, and 0.05) precursor solutions were prepared by sol-gel synthesis using Zn, and Er based alkoxide which were dissolved into solvent and chelating agent. Zn1-xErxO thin films with different Er doping concentration were grown on glass substrate using sol-gel dip coating. Thin films were annealed at 600 °C for 30 min, and tried to observe the effect of doping ratio on structural and optical properties. The particle size, crystal structure, surface morphologies and microstructure of all samples were characterized by X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM). The UV-vis spectrometer measurements were carried out for the optical characterizations. The surface morphology of the Zn1-xErxO films depend on substrate nature and sol-gel parameters such as withdrawal speed, drying, heat treatment, deep number (film thickness) and annealing condition. Surface morphologies of Er doped ZnO thin films were dense, without porosity, uniform, crack and pinhole free. XRD results showed that, all Er doped ZnO thin films have a hexagonal structure and (002) orientation. The optical transmittance of rare earth element (Er) doped ZnO thin films were increased. The Er doped ZnO thin films showed high transparency (>85) in the visible region (400-700 nm).
Microstructural and electrical characterizations of transparent Er-doped ZnO nano thin films prepared by sol–gel process
(2017-10-01) Asikuzun E.; Ozturk O.; Arda L.; Terzioglu C.
In this study, rare earth element (Er) doped ZnO nano thin films which have dual structure of (Zn1−xErx)O (x = 0.0, 0.01, 0.02, 0.03, 0.04 and 0.05) are prepared by using sol–gel method. The microstructure and electrical properties of prepared nano thin films are investigated. Nano thin films are coated on the glass substrate by using the dip coating method. The films are annealed at 600 °C for 30 min. The X-ray diffractometer (XRD), scanning electron microscopy and atomic force microscopy are used to determine the structural properties such as crystal structures, grain sizes, surface morphology; Hall effect measurements system is used to investigate the electrical properties of materials. XRD results showed that all Er doped nano thin films have a hexagonal structure and (002) orientation. Surface morphologies of ZnErO thin films are denser and more uniform than the undoped ZnO thin film. According to the Hall effect measurements, the resistivity of the films decreased with increasing Er concentration from 0 to 4 % and then slightly increased at 5 % Er.
Nanostructural characterization and defect-mediated room temperature ferromagnetism of Zn1−xFexO (x = 0.00–0.07) nanorods prepared via hydrothermal method
(2021-11-05) Kaya S.; Ozturk O.; Arda L.; Bulut F.
The effect of Iron (Fe) doping on crystal structure, morphology, optical behavior, and magnetism of Zn1−xFexO (x = 0.00, 0.01, 0.03, 0.05, 0.07) nanorods prepared via a hydrothermal method was investigated. According to the X-ray diffraction results, Fe ions were incorporated successfully into the Zn ions sites without any deterioration in the wurtzite crystal structure. According to the photoluminescence spectra, a relative increment was observed in the intensity of the near band edge emissions as the Fe concentration increased. Deep level emissions showed that the yellow-orange and violet emissions, corresponding to the oxygen vacancies and zinc interstitials, respectively, increased with the Fe doping. Magnetic measurement results indicated that the undoped ZnO nanorods are diamagnetic. Room temperature ferromagnetism was observed in the Fe doped ZnO nanorods regardless of the doping rate. Although there was no logical relationship between the saturated magnetic moments and the Fe concentration, an obvious correlation was observed between the concentration of point crystal defects including oxygen vacancies, zinc interstitials, and the ferromagnetic parameters. The defect-mediated interactions and the bound polarons effect are suggested for the possible origins of room temperature ferromagnetism in Fe doped ZnO nanorods. The results of the study also provide detailed data for the production method of the ZnO nanorods with enhanced structural, optical and ferromagnetic properties, which are promising candidates for spintronic device applications in nanoelectronics.
Preparation, growth and characterization of nonvacuum Cu-doped ZnO thin films
(2018-08-05) Asikuzun E.; Ozturk O.; Arda L.; Terzioglu C.
We investigated the effects of increasing Cu dopant concentration on the microstructure and optical properties of Zn1−xCuxO thin films. The transparent Zn1−xCuxO solution concentrations were varied from x = 0.0 to x = 0.05 with an increment of 0.01. All nano films were prepared by dip coating system using the sol-gel method. X-ray diffraction (XRD) measurements, scanning electron microscopy (SEM) observations, energy-dispersive X-ray spectroscopy (EDS) analyses, and atomic force microscopys (AFM) analyses revealed a fine-grained structure resulting from doping of Cu into the ZnO structure. In addition, UV–Vis spectrophotometer was used to determine the optic properties of ZnO based nano thin films. XRD analysis also showed that the undoped ZnO and Cu-doped ZnO films oriented along the (002) as the dominant plane. In the 400–700 nm wavelength range, a decrease in transparency was observed in the Zn1−xCuxO thin films with increasing Cu concentration. Although the optical band gap of the Cu-doped ZnO thin films was lower than that of the undoped ZnO thin film, the Urbach energy of the all of the doped thin films was higher than the undoped ZnO thin film.
Preparation, structural and micromechanical properties of (Al/Mg) co-doped ZnO nanoparticles by sol–gel process
(2015-10-22) Asikuzun E.; Ozturk O.; Arda L.; Akcan D.; Senol S.; Terzioglu C.
Zn0.90Mg0.10−xAlxO (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.10) nanoparticles were prepared by using sol–gel technique. The effects of Al and Mg doping on the structural and mechanical properties were investigated by using X-Ray diffraction (XRD), scanning electron microscopy (SEM) and digital micro-hardness tester, respectively. The grain size, a and c lattice parameters and morphology of nanoparticles were characterized by XRD and SEM measurements. The grain sizes of Al/Mg co-doped ZnO nanoparticles were also calculated by Scherrer–Warren equation. a and c lattice parameters are calculated from XRD peaks. According to the results it was observed that the grain sizes increased with increasing the Al doping. c lattice parameter partially decreased with Al doping. The experimental results of hardness measurements were analyzed using Meyer’s law, proportional specimen resistance model, elastic/plastic deformation model, and Hays–Kendall (HK) approach. It was observed that HK approach is the most successful model for the micro-hardness analysis of Al/Mg co-doped ZnO materials.
Roughness and bearing analysis of ZnO nanorods
(2020-07-01) Kaya S.; Ozturk O.; Arda L.
It is essential to analyze the surfaces of thin films precisely to control the production process and the performance of nano-scale devices. Conventional techniques give limited information about the nano-scale surface morphology. Instead, atomic force microscopy (AFM) provides more accurate results about the surface parameters of nanostructures. Hence, in the current study, two-dimensional (2D) and three-dimensional (3D) morphological properties of zinc oxide (ZnO) nanorods (NRs) were investigated using AFM. ZnO NRs were produced via a hydrothermal method at different growth times and temperatures. The surface texture was also examined by scanning electron microscopy (SEM). The results revealed that the morphological parameters such as diameter, length, and shape of the nanorods could be tuned by changing growth time and temperature. Moreover, we analyzed the most crucial roughness and bearing analysis parameters, which affect the functional properties of ZnO in the surface engineering applications. The average roughness increased from 5.86 nm to 17.30 nm as growth time increased from 2 h to 5 h. The average roughness was obtained as 10.92 nm for the temperature of 90 °C and it reached 41.13 nm for 150 °C. In addition, height distribution and bearing area curves associated with the real contact area were reported. 90% of the area was spread at a depth of 48 nm for the growth time of 2 h while this value was obtained 183 nm for 5 h Addition, 90% of the area was spread at a depth of 88 nm and 457 nm for the temperature of 90 °C and 150 °C, respectively. We believe that our study would be a pioneering perspective on bearing analysis of ZnO nanorods.
Structural and mechanical properties of (Co/Mg) co-doped nano ZnO
(2015-06-01) Asikuzun E.; Donmez A.; Arda L.; Cakiroglu O.; Ozturk O.; Akcan D.; Tosun M.; Ataoglu S.; Terzioglu C.
The (Co/Mg) co-doped ZnO systems (ZnMgCoO) were synthesized as polycrystalline nanoparticles using the sol-gel technique. The effects of Co/Mg co-addition to the structural and mechanical properties of ZnO nanoparticles were investigated. Microstructural properties, such as phases, crystal structures and grain sizes are characterized by using X-Ray Diffraction (XRD) analysis and Scanning Electron Microscope (SEM). The microhardness values of the samples were evaluated by the Vickers tester. In the samples of the Co>Mg ratio, Indentation Size Effect (ISE) behaviors were observed. On the other hand, in the samples of the Mg>Co ratio, Reverse Indentation Size Effect (RISE) was observed. These were analyzed in detail utilizing the models for materials hardness analysis found in literature.
Structural and mechanical properties of transition metals doped ZnMgO nanoparticles
(2013-02-01) Arda L.; Ozturk O.; Asikuzun E.; Ataoglu S.
Zn0.94Mg0.01TM0.05O (TM=Ni, Co, Mn, and Cr) solutions were synthesized by the sol-gel technique using Zn, Mg, Ni, Co, Mn, and Cr based alkoxide. The effects of doping transition metals and annealing temperature on structure and mechanical properties of the ZnMgO nanoparticles were systematically investigated. The phases, crystal structures, sizes and microstructures of the samples were characterized using X-ray diffraction and scanning electron microscope. Microhardness values were measured using a digital Vickers microhardness tester. The experimental results were analyzed using Kick's Law, Proportional Specimen Resistance (PSR), Elastic/Plastic Deformation (EPD) models, and Hays-Kendall (HK) approach. The microhardness values of Ni, Co, Mn, and Cr doped ZnMgO nanoparticles gradually decreased, respectively. The Indentation Size Effect behavior was observed. The grain sizes of ZnMgNiO, ZnMgCoO, ZnMgMnO, and ZnMgCrO nanoparticles were calculated approximately to be 26.36, 26.22, 22.89, and 19.24nm using the Sherrer equation, respectively. © 2012 Elsevier B.V.
Structural and mechanical properties of ZnMgO nanoparticles
(2014-01-10) Tosun M.; Ataoglu S.; Arda L.; Ozturk O.; Asikuzun E.; Akcan D.; Cakiroglu O.
This study reports the effect of annealing temperature on the structure and mechanical properties of Zn0.95Mg0.05O bulk samples by using digital Vickers microhardness tester, X-ray diffraction analysis, scanning electron microscopy and electron dispersive X-ray measurements. The samples were prepared using Zn and Mg based alkoxed by the sol-gel technique and annealed at various temperatures (500, 600, 700 and 800°C). Vickers microhardness, elastic modulus, yield strength and fracture toughness values of Zn0.95Mg0.05O bulk samples were separately calculated and compared with each other. The experimental results of hardness measurements were analyzed using Meyer's law, Proportional Specimen Resistance (PSR) and Elastic/Plastic Deformation (EPD) models and Hays-Kendall (HK) approach. Finally, it was seen that HK approach is the most successful model for the microhardness analysis of these materials. © 2013 Elsevier B.V.
Vertically aligned Nd substituted ZnO nanorods: Morphology, optical characteristics and room temperature ferromagnetism
(2022-03-01) Kaya S.; Ozturk O.; Arda L.
Zn1-xNdxO (x = 0.00, 0.01, 0.03, 0.05, 0.07) nanorods (NRs) are grown vertically, perpendicular to the glass substrate using a hydrothermal method. Nd3+ ions are successfully substituted into the crystal lattice of ZnO. The crystal structure, morphology, optical, and magnetic properties are comprehensively studied by various techniques. Significant changes are observed in the morphological and optical properties of the Nd substituted ZnO NRs. According to the magnetic measurements, the maximum Hc value is observed to be 39.04 Oe at a concentration of 3% Nd and the maximum Ms value is observed to be 20.52 x 10−6 emu at 7% Nd, whereas the maximum Mr value is measured as 1.86 x 10−6 emu at 5% Nd, confirming that the magnitude of magnetic parameters are independent of Nd concentration. An opposing correlation is found between the Hc value and the morphological properties (including crystallite size, average roughness, and aspect ratio) of Nd substituted ZnO NRs.