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Öğe CBD grown ZnO nanostructures: effects of solution temperature(Carl Hanser Verlag, 2013) Kahraman, Suleyman; Cakmak, Haci Mustafa; Cetinkaya, Samed; Cetinkara, Haci Ali; Guder, Husnu SalihIn the present study, textured and highly oriented nano-structured ZnO films were synthesized via chemical bath deposition. The effects of solution temperature have been investigated. It is concluded that the solution temperature is crucial to the crystallography, morphology, electrical and optical behaviors of the ZnO films. X-ray diffraction studies and scanning electron microscopy observations revealed that the structures grown at 95 degrees C had a large aspect ratio, a faster c-axis growth and better vertical orientation than those obtained at relatively lower temperature. The variations depending on solution temperature have been provisionally explained theoretically. Electrical resistivity and activation energies of the films decreased with increasing solution temperature. The variation was attributed to enhancement in the crystallographic structure with increasing growth temperature and to delocalized phonon states. Through the optical absorption spectra a red shift was observed and attributed to crystal defects, non-stochiometry that Zn+2 ions substitute oxygen vacancies and delocalized phonon states.Öğe Cu2SnS3 absorber thin films prepared via successive ionic layer adsorption and reaction method(Carl Hanser Verlag, 2013) Kahraman, Suleyman; Cetinkaya, Samed; Cakmak, Haci Mustafa; Cetinkara, Haci Ali; Guder, Husnu SalihIn this paper, we report the production of Cu2SnS3 thin films with high phase purity via successive ionic layer adsorption and reaction method on soda lime glass substrates. Structural, morphological, compositional, optical and electrical investigations were carried out. The X-ray diffraction patterns of the samples matched very well with the reference pattern and proved the polycrystalline nature of the films. As a secondary phase, one weak peak indicating covallite Cu2-xS phase was observed in the pattern of the sample deposited by using equimolar Cu and Sn. The surface morphologies of the films were found to be continuous and composed of homogeneously distributed large grains. From the reflectance and transmittance data, the optical absorption coefficient values of the films were found to be about 10(4) cm(-1) and the films were found to be almost opaque in the wavelengths from 200 to 600 nm with a small reflectivity of about 10%. Band gap values of the films decreased from 1.45 to 1.35 eV with decreasing Cu content. Electrical characterization showed that the films were p-type semiconductor. Two different impurity levels for each film were found via resistivity-temperature characteristics.Öğe Effects of annealing on morphological, structural and electrical properties of thermally evaporated WO3 thin films(Academic Press Ltd- Elsevier Science Ltd, 2012) Usta, Metin; Kahraman, Suleyman; Bayansal, Fatih; Cetinkara, Haci A.Tungsten trioxide (WO3) thin films were prepared by thermal evaporation method onto quartz substrates at room temperature. Effect of annealing temperature (from 200 to 800 degrees C) to morphology, crystallographic structure and electrical properties were investigated. In order to investigate the temperature dependant resistivity properties of the films dark current-voltage measurements were done at the temperatures of 30, 60, 90, 120 and 150 degrees C. From the AFM pictures it is seen that the increasing annealing temperature causes an increase in grain sizes. At elevated temperatures the grains combine to each other and thus form continuous and homogenous surfaces. From the XRD patterns it was seen that the as-prepared and annealed films at 200, 300, 310 and 320 degrees C were amorphous. On the other hand at 330 degrees C and higher temperatures the films were found as in crystallized structures (monoclinic phase). From the current-voltage measurements it was seen that the contacts areohmic and the current increased with increasing temperatures. From the calculated values it was seen that the produced films shows good semiconducting nature. (C) 2012 Elsevier Ltd. All rights reserved.Öğe The effects of coumarin additive on the properties of CdS thin films grown by chemical bath deposition(Elsevier Sci Ltd, 2015) Yucel, Ersin; Kahraman, SuleymanCdS thin films have been obtained on glass substrates by using chemical bath deposition technique. Different concentrations of coumarin were used as an additive in the growth solutions, for the first time. The effects of coumarin on the properties of the as-deposited and annealed CdS thin films were investigated. It was found that increasing coumarin concentration in the growth solution remarkably affects the crystallinity and uniformity of the films. The 1% and 2% presence of coumarin enhanced the surface morphology while higher concentrations decreased surface uniformity. In the optical band gap values of both as-deposited and annealed films, a decrease has been observed with increasing additive concentration. Through temperature dependent resistance measurements of the films, impurity levels' electrical activation energies for each film have been estimated by means of the obtained discrete linear regions indicating different conduction mechanisms. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Facile Synthesis of Cu2ZnSnS4 Photovoltaic Absorber Thin Films via Sulfurization of Cu2SnS3/ZnS Layers(Springer, 2014) Kahraman, Suleyman; Podlogar, Mateja; Bernik, Slavko; Guder, Husnu SalihCopper zinc tin sulfide (Cu2ZnSnS4) has been receiving a lot of attention in recent years as a new, alternative absorber for the production of cheap thin film solar cells owing to the high natural abundance of all the constituents, its tunable direct-band-gap energy, and its 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, Cu2ZnSnS4 thin films were grown on soda lime glass substrates via the sulfurization of solution grown Cu2SnS3/ZnS stacked sulfide layers. A new facile route to overcome the difficulty of depositing Cu2ZnSnS4 thin film with a desired stoichiometric composition in a single cation solution has been presented. The influences of deposition cycles of layers on the morphological, compositional, structural, and optical properties of the samples were investigated. It was observed from scanning electron microscopy (SEM) images that the films were continuous and composed of homogenously distributed large grains. Possible chemical formulations of the best samples were predicted to be Cu1.99Zn1.25Sn1.00S3.76 and Cu1.97Zn1.03Sn1.29S3.71 via energy-dispersive X-ray spectroscopy (EDXS) results. The X-ray diffraction (XRD) patterns of the samples matched very well with the reference values. The Raman-scattering analysis of the films proved the phase purity of the CZTS samples. The optical absorption coefficient of the films was found to be about 10(4) cm(-1) based on absorbance spectroscopy. The optical band gaps of the films were estimated to be between 1.36 and 1.50 eV. From these we are able to conclude that CZTS thin films can be effectively obtained via the vacuum-atmosphere sulfurization of Cu2SnS3/ZnS stacked sulfide layers. (C) The Minerals, Metals & Materials Society and ASM International 2013Öğe Performance of two low-cost GPS receivers for ground speed measurement under varying speed conditions(Springer, 2017) Keskin, Muharrem; Sekerli, Yunus Emre; Kahraman, SuleymanA global positioning system (GPS) receiver is an important sensor used in modern farming, particularly in precision agriculture to determine geographic location and ground speed. The aim of this study was to investigate the effectiveness of two low-cost GPS receivers for measuring ground speed under varying speed conditions on four different dates. A rotary shaft encoder on an auxiliary wheel mounted on an agricultural tractor was used as a reference. A significant time lag between the rotary encoder speed and the GPS speed was found over a range of speeds. It was observed that the GPS speed lagged the encoder speed in both increasing and decreasing speeds. The average time lag was found to be between 3.6 and 5.2 s for Receiver 1 while Receiver 2 had a time lag from 1.7 to 2.5 s. A significant difference was found between the two receivers for increasing and decreasing speeds in terms of time lags (P < 0.05). A post correction by shifting the GPS speed increased the accuracy of the speed measurement capability of both receivers resulting in an average correlation coefficient of 0.30-0.90 for Receiver 1 and 0.65-0.98 for Receiver 2. Effect of USB-to-COM converter was also studied and it did not have a significant effect on time delay. The GPS receivers provided reliable data during constant speed operating conditions; however, caution should be exercised in varying speed conditions when using low-cost GPS receivers. Also, the companies that produce GPS-based speed sensors should supply technical specifications related to velocity estimates during acceleration and deceleration.Öğe Synthesis, characterization and humidity sensing properties of Mn0.2Ni0.8Fe2O4 nanoparticles(Elsevier Science Sa, 2013) Koseoglu, Yuksel; Aldemir, Ismail; Bayansal, Fatih; Kahraman, Suleyman; Cetinkara, Haci AliMn0.2Ni0.8Fe2O4 nanoparticles were synthesized by PEG assisted hydrothermal technique. XRD and FT-IR analysis confirmed the composition and structure as spinel ferrite. The average crystallite size was found as 27 nm from the XRD pattern. SEM measurements have revealed that the nanoparticles exhibit large grain structures having regular morphology (polygons) with soft agglomerations. Gas sensing characteristics of the film fabricated by Mn0.2Ni0.8Fe2O4 nanoparticles were investigated for different concentrations of humidity, ethanol, acetone, methanol, toluene and benzene and for oxygen gas. It was found that the sensor is highly sensitive to humidity but weakly sensitive for the other organic volatile compounds and especially for oxygen gas. (C) 2013 Elsevier B.V. All rights reserved.Öğe Using Raman Spectroscopy for Determination Methanol Quantity in Illegal Alcoholic Beverages(Office Spectroscopy & Spectral Analysis, 2017) Zeren, Cem; Acikgoz, Gunes; Kahraman, SuleymanIllegal production of alcoholic beverages is a common problem in most countries. The consumption of these counterfeit alcoholic products in Turkey has increasingly been one of the major health concerns. In this study, a comparison between GC-MS and Raman spectroscopy techniques was made to determine the amount of methanol in BogmaRaki which is a counterfeit alcoholic beverage produced and consumed in Hatay region. Different ratios of methanol/ethanol concentrations were prepared to obtain a calibration curve. This curve was used to measure the amount of methanol in the actual product samples using both GC-MS and Raman spectroscopy techniques. Results obtained from both techniques were compared using Paired sample t-tests. The Limit of Detection and the Limit of Quantification values were determined as 0. 03 (%v/v) and 0. 11 (v/v), respectively. Both techniques demonstrated a similar sensitivity in the determination of methanol concentration in these counterfeit products (p>0.05). Raman Spectroscopy, however, has an advantage of being easy to use, inexpensive, rapid and non-destructive analytical technique with little or no sample preparation.
