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Öğe Alloying effect on K X-ray intensity ratio and production cross section values of Zn and Cr in Zn-Cr alloys(Pergamon-Elsevier Science Ltd, 2013) Dogan, M.; Tirasoglu, E.; Karahan, I. H.; Aylikci, N. Kup; Aylikci, V.; Kahoul, A.; Cetinkara, H. A.In this study, sigma(K alpha), sigma(K beta) production cross-sections and K-beta/K-alpha intensity ratios of Cr and Zn have been measured in pure metals and in different alloy compositions which have different composition values. And also, empirical and semi-empirical K-shell fluorescence yields (omega(K)) and K-beta/K-alpha intensity ratios from the available experimental data for elements with 23 <= Z <= 30 were calculated. The experimental data are fitted using the quantity (omega(K)/(1-omega(K)))(1/4) vs. Z to deduce the empirical K-shell fluorescence yields and K-beta/K-alpha intensity ratios. The effects of alloying on the fluorescence parameters and bath temperatures on alloy compositions were investigated. Our analysis indicates that these effects arise from reorganization of atom and charge transfer mechanism in alloys. (c) 2013 Elsevier Ltd. All rights reserved.Öğe Alloying effect on K X-ray intensity ratio and production cross section values of Zn and Cr in Zn-Cr alloys (vol 87, pg 6, 2013)(Pergamon-Elsevier Science Ltd, 2015) Dogan, M.; Tirasoglu, E.; Karahan, I. H.; Aylikci, N. Kup; Aylikci, V.; Kahoul, A.; Cetinkara, H. A.[Abstract Not Available]Öğe Characterisation of ZnO nanorod arrays grown by a low temperature hydrothermal method(Taylor & Francis Ltd, 2012) Kahraman, S.; Cetinkara, H. A.; Bayansal, F.; Cakmak, H. M.; Guder, H. S.In this paper, growth steps of well defined ZnO nanorod arrays deposited on seeded substrates were investigated. To obtain ZnO seed layer on glass substrates, a successive ionic layer adsorption and reaction (SILAR) method was used and then ZnO nanorods were grown on seed layer using a chemical bath deposition (CBD) method. The effects of seed layer and deposition time on morphology, crystallographic structure (e.g. grain size, microstrain and dislocation density) and electrical characteristics of ZnO nanorods were studied. From the SEM micrographs, it could be seen that the ZnO nanorods densely covered the substrate and were nearly perpendicular to the substrate surface. The XRD patterns showed that the ZnO nanorod arrays had a hexagonal wurtzite structure with a preferred orientation along the (002) plane. An increase in deposition time resulted in an increase in the intensity of the preferred orientation and grain size, but a decrease in microstrain and dislocation density. Electrical activation energies of the structures were calculated as 0.15-0.85 eV from current-temperature characteristics. It was concluded that the morphologies of the structures obtained in this study via a simple and fast solution method can provide high surface areas which are important in area-dependent applications, such as solar cells, hydrogen conversion devices, sensors, etc.Öğe Characteristics of ZnO thin films doped by various elements(Elsevier Science Bv, 2013) Kahraman, S.; Cakmak, H. M.; Cetinkaya, S.; Bayansal, F.; Cetinkara, H. A.; Guder, H. S.We have investigated the effects of Al, K and Co dopant elements on the properties of ZnO thin films deposited by CBD method on glass substrates. Changing in morphology, structural parameters, ionization energies of impurity levels, absorption behavior and optical band gap values were investigated through scanning electron microscopy (SEM), X-Ray diffraction (XRD), resistance-temperature measurement (R-T) and ultraviolet-visible spectroscopy (UV-vis) techniques. From the SEM observations, various morphologies (rod-like, flower-like and rice-like) were observed. Those morphological variations were attributed to the change in stable growth mechanism of intrinsic ZnO, induced by different atomic radius and different electronegativity of dopants. XRD results indicated that all orientations are well indexed to hexagonal phase crystalline ZnO. The impurity level ionization energy values (Delta E) were estimated as 0.32/0.13/0.07 eV; 0.34/0.15 eV; 0.40/0.13 eV and 0.48/0.22 eV for the Al, K, Co doped samples and i-ZnO, respectively. Optical band gap values were found that the doped samples' were higher than the intrinsic one's. This increasing (blue shift) was attributed to a deterioration which occurred in the lattice of the structures after doping. This effect was also supported by the structural results. (C) 2012 Elsevier B.V. All rights reserved.Öğe Characterization of Al/n-ZnO/p-Si/Al structure with low-cost solution-grown ZnO layer(Taylor & Francis Ltd, 2013) Cetinkaya, S.; Cetinkara, H. A.; Kahraman, S.; Bayansal, F.We report the fabrication of Al/n-ZnO/p-Si/Al diode structures with a flower-like ZnO layer. The average grain size, microstrain and dislocation density in the ZnO layer were determined as 25nm, 1.55x10(-3) and 3.23x10(13)cm(-2), respectively. From absorption spectra, the optical band gap was found to be approximate to 3.17eV. A red shift was attributed to non-stoichiometry arising from Zn+2 ions substituting for oxygen vacancies. The ideality factor was determined as 1.55. The barrier height was calculated as 0.71eV from I-V characteristics and 0.73eV using the Norde plots.Öğe Characterization of CBD grown ZnO films with high c-axis orientation(Elsevier Science Sa, 2012) Kahraman, S.; Bayansal, F.; Cetinkara, H. A.; Cakmak, H. M.; Guder, H. S.Highly c-axis oriented ZnO films were deposited on seeded glass substrates. Successive ionic layer adsorption and reaction (SILAR) method and chemical bath deposition (CBD) method were used to obtain seed layers and ZnO films. To see the effects of seed layer and deposition time, structural (e.g. grain size, microstrain and dislocation density), morphological, and electrical (e.g. resistivity, activation energy) properties of the films were investigated by scanning electron microscopy, X-ray diffraction, and four point probe method. From the SEM images, resultant structures were found as well defined nanorods nearly perpendicular to the substrate surfaces and densely cover the substrates. The XRD patterns showed that ZnO films have hexagonal wurtzite structure with a preferred c-axis orientation along (002) plane. C-axis orientation was also supported by texture coefficient calculations. The lattice parameters of the structures were determined as a = 3.2268 angstrom, b = 5.2745 angstrom, alpha = beta = 90 degrees and gamma = 120 degrees. From the XRD patterns, it was revealed that, microstrain and dislocation density values of the structures decreased whereas grain size increased. This was attributed to enhancement occurred in lattice structure of the ZnO films. Activation energy values of the films were found in between 0.12 and 0.15 eV from the dark electrical resistivity-temperature characteristics in a temperature range of 300-500 K. (c) 2012 Elsevier B.V. All rights reserved.Öğe A comparative study of Cu2ZnSnS4 thin films growth by successive ionic layer adsorption-reaction and sol-gel methods(Elsevier Science Sa, 2014) Kahraman, S.; Cetinkaya, S.; Cetinkara, H. A.; Guder, H. S.Owing to the high natural abundance and non-toxicity of all the constituents, the copper-zinc-tin-sulfide compound has been attracting attention in recent years for the production of cheap solar absorber materials. Solution-based low-cost approaches are being developed for the deposition of this compound. In this comparative study, we have investigated Cu2ZnSnS4 thin films prepared by using successive ionic layer adsorption-reaction and sol-gel methods. X-ray diffraction studies indicated the polycrystalline nature of the films. No secondary phases were observed. The sol-gel grown Cu2ZnSnS4 film was found to have smaller crystallite size and higher microstrain and dislocation density values. Phase purity and good crystalline quality of the studied films were proved through the Raman studies. From the scanning electron microscopy images, sol-gel grown Cu2ZnSnS4 film was found to have more homogenous and smooth morphology. Possible chemical formula of the films was determined. The optical absorption of the sol-gel grown film covered a wider wavelength range by means of absorbing more visible photons. The optical band gap values were estimated to be 1.45 and 1.40 eV for the successive ionic layer adsorption-reaction and sol-gel grown samples, respectively. It was concluded that both methods are effective and can be used to produce high-quality Cu2ZnSnS4 thin films for cheap and green solar cell applications. (C) 2013 Elsevier B. V. All rights reserved.Öğe CuO nanostructures grown by the SILAR method: Influence of Pb-doping on the morphological, structural and optical properties(Elsevier Science Sa, 2015) Bayansal, F.; Gulen, Y.; Sahin, B.; Kahraman, S.; Cetinkara, H. A.CuO nanostructures with and without Pb were synthesized by the Successive Ionic Layer Adsorption and Reaction method. The films were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and ultraviolet-visible spectrophotometry. Scanning electron microscopy results showed that the morphology of the film surface was changed from plate-like to coral-like nanostructures with increasing Pb concentration. The X-ray diffraction patterns showed the monoclinic crystal structure with preferential planes of ((1) over bar 11) and (111). Furthermore, ultraviolet-visible spectra showed that the band gap of the films was tailored by Pb doping. (C) 2014 Elsevier B.V. All rights reserved.Öğe Effect of coumarin concentration on the physical properties of CdO nanostructures(Elsevier Sci Ltd, 2014) Sahin, B.; Bayansal, F.; Yuksel, M.; Biyikli, N.; Cetinkara, H. A.In this work, nanostructured CdO films with different coumarin contents in the growth solution were fabricated on glass substrates by the HEAR method. The effects of coumarin content in the bath on optical, structural and morphological properties were studied by means of (UV-vis) spectrophotometer, SEM and XRD analysis. The analysis showed that the band gaps, surface morphologies and XRD peak intensities of the CdO films were found to change with coumarin content. A change in the band gap energy can be attributed to the improvement in crystallinity of the samples. XRD analysis showed that, the films have poly-crystalline structures with decent crystallinity levels. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Effect of heat treatment on the properties of Cd(OH)2 and CdO films grown by chemical bath deposition(Taylor & Francis Ltd, 2013) Sahin, B.; Bayansal, F.; Cakmak, H. M.; Kahraman, S.; Cetinkara, H. A.Nanostructured cadmium hydroxide (Cd(OH)2) thin films have been fabricated on glass substrates by the chemical bath deposition method and converted into cadmium oxide (CdO) films by heat treatments. Some of the films were studied as-grown and the others were annealed in air at 150, 300 and 450 degrees C. The effects of various annealing processes on the structural, morphological and optical properties of the Cd(OH)2 and CdO films were studied. The band gaps of the films vary from 2.74eV to 2.32eV for different annealing temperatures. It was observed that there is a direct dependence of the structural, morphological and optical properties on the annealing temperature of the films. X-ray diffraction (XRD) measurements showed that as-grown and annealed film at 150 degrees C fully consist of Cd(OH)2 and the annealed films at 300 and 450 degrees C consist of CdO nanoparticles. The size of the nanoparticles, which were calculated from the scanning electron microscopy (SEM) figures by using a pixels program, was found to lie between 460 and 600nm.Öğe The effects of coumarin additive on the properties of ZnO nanostructures(Pergamon-Elsevier Science Ltd, 2013) Kahraman, S.; Cakmak, H. M.; Cetinkaya, S.; Cetinkara, H. A.; Guder, H. S.In this study, we investigated the effects of coumarin presence in the growth solution on the properties of ZnO. Significant changes/improvements were observed in morphology and crystal structure. From the morphological studies, it was seen that the substrates were uniformly covered with rod/rice-like nano-structures and average diameters of the structures decreased with increasing coumarin content in the growth solution. Also coumarin affected the surface morphology, coverage density and uniformity of the shape of the structures. The X-ray diffraction patterns indicated that all diffraction peaks were well indexed to hexagonal phase crystalline ZnO. The greater intensities of (0 0 2) peaks in the patterns revealed c-axis orientation normal to the substrate. The crystallization of the samples was gradually enhanced with increasing coumarin volume up to 5%. When the coumarin volume exceeded 5%, the crystallization was affected negatively. The electrical resistivity values increased with increasing coumarin content and it was attributed to the decrease in carrier concentration originated by carrier traps at the grain boundaries. (C) 2012 Elsevier Ltd. All rights reserved.Öğe Effects of diethanolamine on sol-gel-processed Cu2ZnSnS4 photovoltaic absorber thin films(Pergamon-Elsevier Science Ltd, 2014) Kahraman, S.; Cetinkaya, S.; Cetinkara, H. A.; Guder, H. S.As a promising solar absorber, the Cu2ZnSnS4 compound has been popular recently for the production of green and economical thin-film solar cells owing to the abundancy and non-toxicity of all the constituents. In this study, we have produced Cu2ZnSnS4 films via the sal-gel technique. As a stabilizer, the effects of the diethanolamine on the properties of the films were investigated. The amount of diethanolamine significantly affected the crystal structure, crystallite sizes and phase purity of the films. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of phase-pure CZTS films. It was found that the film produced by using 2 ml of diethanolamine in sol exhibited pure CZTS phase, compact and dense morphology and enhanced photo-sensitivity. Light on/off current ratio of the n-Si/Cu2ZnSnS4 junction was found to be 47 under 100 mW/cm(2) of illumination. Electrical activation energies of the films were investigated and the variations were attributed to delocalized phonon states generating from the presence of other phases and lattice defects. (C) 2013 Elsevier Ltd. All rights reserved.Öğe Effects of the sulfurization temperature on sol gel-processed Cu2ZnSnS4 thin films(Elsevier Sci Ltd, 2013) Kahraman, S.; Cetinkaya, S.; Podlogar, M.; Bernik, S.; Cetinkara, H. A.; Guder, H. S.As a promising and alternative solar absorber material, the copper zinc tin sulfide compound (Cu2ZnSnS4) has been drawing attention in recent years for the production of cheap thin-film solar cells owing to the high natural abundance and non-toxicity of all the constituents, a tunable direct-band-gap energy and a large optical absorption coefficient. In addition, to overcome the problem of expensive vacuum-based methods, solution-based approaches are being developed for Cu2ZnSnS4 deposition. In this study, we have produced Cu2ZnSnS4 thin films via the sol gel technique and subsequent sulfurization. The effects of the sulfurization temperature on the structural, morphological, compositional and optical properties of the films were investigated. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of phase-pure CZTS films. The crystallinity of the films increased with an increasing sulfurization temperature. From the surface images and the results of the composition analysis, it was found that the films are uniform, composed of homogenously distributed grains and have compositions with Cu deficit. The values of the optical absorption coefficients for the films were found to be 10(4) cm(-1) based on absorbance spectroscopy. The optical band-gap values were estimated to be between 1.32 and 2.27 eV depending on the sulfurization temperature. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Effects of thermal oxidation temperature on vacuum evaporated tin dioxide film(Academic Press Ltd- Elsevier Science Ltd, 2012) Cakmak, H. M.; Cetinkara, H. A.; Kahraman, S.; Bayansal, F.; Tepe, M.; Guder, H. S.; Cipiloglu, M. A.In order to investigate the effect of thermal oxidation temperature on tin dioxide (SnO2), tin dioxide films were obtained on quartz substrates by vacuum evaporation of tin metal. The films were characterized by X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM), temperature dependent electrical resistivity measurement and optical absorption spectroscopy. The SEM images showed that the films are dense, continuous and are composed of nanoparticles and particle sizes are increased after thermal oxidation. From the X-ray measurement results, the films indicated two strong reflection peaks of tetragonal structure in the orientations of (101) and (200) at 20 = 33.8 degrees and 37.95 degrees, respectively. Intensity of the peaks increased with increasing thermal oxidation temperature. We found resistivity values of about 10(-4) Omega-cm. Optical absorption spectra of the films in the UV-Vis spectral range revealed that optical band gap (E-g) value of the films increases with increasing thermal oxidation temperature. (C) 2012 Elsevier Ltd. All rights reserved.Öğe Electrodeposition and characterisation of Zn, Zn-Fe and Zn-Fe-Ni coatings in presence of gelatin as additive(Taylor & Francis Ltd, 2008) Karahan, I. H.; Cetinkara, H. A.; Gueder, H. S.Studies of the factors that enhance the corrosion behaviour of electrodeposited Zn, Zn-Fe and Zn-Fe-Ni coatings are highly relevant due to the considerable industrial use of these alloys as protective coatings for steel substrates. This paper reports on the corrosion behaviour and structure of Zn, Zn-Fe and Zn-Fe-Ni coatings deposited from an acid citrate solution studied in the absence and in the presence of gelatin as additive. The presence of Fe or Fe-Ni in the Zn matrix increases Zn coating corrosion resistance. The presence of gelatin in the plating bath increases the corrosion resistance of Zn, Zn-Fe and Zn-Fe-Ni coatings.Öğe Fabrication and characterization of Mn-doped CuO thin films by the SILAR method(Elsevier Sci Ltd, 2013) Gulen, Y.; Bayansal, F.; Sahin, B.; Cetinkara, H. A.; Guder, H. S.Thin films of un-doped and Mn-doped CuO nanostructures have been deposited on glass substrates via the SILAR method. The morphological, compositional, structural and optical properties of the films have been investigated by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction analysis and UV vis spectrophotometry. The analyzed results indicate that the obtained films consist of plate-like nanostructures. From the EDS analysis it is seen that Mn-doping concentration affects the shapes of the nanostructures. XRD results show that all of the films have monoclinic structure. From the room temperature UV-viS analysis it is found that the optical band gap of the films increases with increasing Mn-doping concentrations. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Growth and Characterization of CuO Nanostructures on Si for the Fabrication of CuO/p-Si Schottky Diodes(Hindawi Publishing Corporation, 2013) Cetinkaya, S.; Cetinkara, H. A.; Bayansal, F.; Kahraman, S.CuO interlayers in the CuO/p-Si Schottky diodes were fabricated by using CBD and sol-gel methods. Deposited CuO layers were characterized by SEM and XRD techniques. From the SEM images, it was seen that the film grown by CBD method is denser than the film grown by sol-gel method. This result is compatible with XRD results which show that the crystallization in CBD method is higher than it is in sol-gel method. For the electrical investigations, current-voltage characteristics of the diodes have been studied at room temperature. Conventional I-V and Norde's methods were used in order to determine the ideality factor, barrier height, and series resistance values. It was seen that the morphological and structural analysis are compatible with the results of electrical investigations.Öğe Growth and humidity sensing properties of plate-like CuO nanostructures(Taylor & Francis Ltd, 2014) Bayansal, F.; Cetinkara, H. A.; Cankaya, G.This paper describes a simple, low-temperature and cost-effective liquid-phase method to synthesize homogenous plate-like CuO nanostructures and their sensitivity to humidity. Scanning electron microscopy illustrated that the synthesized CuO nanoplates have thicknesses of ~100 nm. X-ray diffraction measurements showed that the CuO nanostructures have high crystallinity with monoclinic crystal structure preferentially in and directions. From the temperature-dependant dark electrical resistivity measurements, the ionization energies of the impurity levels and thermal band gap energies of the films are found as 0.30, 0.32 and 1.37, 1.39 for as-synthesized and annealed films, respectively. Gas sensing characteristics of the films were investigated for different concentrations of humidity, isopropyl alcohol, methanol, ethanol, chloroform and acetone vapours. It was found that the sensor is sensitive to humidity but not to the other volatile organic compounds.Öğe Growth of homogenous CuO nano-structured thin films by a simple solution method(Elsevier Science Sa, 2011) Bayansal, F.; Kahraman, S.; Cankaya, G.; Cetinkara, H. A.; Guder, H. S.; Cakmak, H. M.This paper describes a simple, low temperature and cost effective solution method to synthesize homogenous cupric oxide (CuO) nano-structured thin films. By this method dense and continuous CuO films with good crystallinity can be prepared in a short time, e.g., in 15 min. The scanning electron microscopy illustrated that the synthesized CuO plate-like nanostructures have RMS thicknesses of 100 nm. The XRD measurements showed that the synthesized CuO nanostructures have a high crystallinity with monoclinic crystal structure preferentially in ((1) over bar 1 1) and (1 1 1) directions. From the temperature dependant dark electrical resistivity measurements the ionization energies of the impurity levels and thermal band gap energies of the films were calculated. (C) 2010 Elsevier B.V. All rights reserved.Öğe Influence of annealing to the properties of un-doped and Co-doped CdO films(Elsevier Sci Ltd, 2014) Sahin, B.; Bayansal, F.; Yuksel, M.; Cetinkara, H. A.Un-doped and Co-doped CdO nanostructures were deposited on glass substrates by successive ionic layer adsorption and reaction (SILAR) method and annealed at 300 and 400 C. Morphological, structural and optical properties of the films were investigated by scanning electron microscope (SEM), X-ray diffractometer (XRD) and ultra violet-vis (UV-vis) spectrophotometry. The analyzed results indicate that Co-doping concentration and annealing temperature affect the properties of nanostructure cadmium oxide (CdO) films. XRD results showed that all of the films are polycrystalline cubic CdO with good crystallinity levels. With UV-vis. analysis at the room temperature it was found that the doping and annealing temperature changed optical properties of CdO films. (C) 2013 Elsevier Ltd. All rights reserved.
