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    CBD grown ZnO nanostructures: effects of solution temperature
    (Carl Hanser Verlag, 2013) Kahraman, Suleyman; Cakmak, Haci Mustafa; Cetinkaya, Samed; Cetinkara, Haci Ali; Guder, Husnu Salih
    In 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.
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    Chemiresistive CuO sensors for label-free C-reactive protein detection
    (Elsevier Science Sa, 2022) Bayansal, Fatih; Cetinkara, Haci Ali
    In this study, we developed fast and highly sensitive, label-free Ca-doped cupric oxide (CuO) based che-miresistive biosensors to detect C-reactive protein (CRP). The Successive Ionic Layer Adsorption and Reaction (SILAR) method was used to deposit pure and Ca-doped CuO thin films on interdigitated gold electrodes. Film surfaces were functionalized with monoclonal anti-C-reactive protein antibody (anti-CRP) by random physisorption method. Sensor fabrication steps were monitored using the linear sweep vol-tammetry method. Scanning electron microscopy was used to investigate the surface morphology. Energy-dispersive X-ray spectroscopy was used to determine the elemental composition. The structure of the films was investigated by the powder X-ray diffractometry method. Sensor parameters were determined by the change in sensor resistance over time. The sensors showed a good response to CRP with a linear detection range of 0.1-5.0 pg/ml, which was within the clinically significant range. Detection limits of 49.61 and 48.81 ng/ml were estimated using the standard deviation of the y-intercept and the standard deviation of the regression line, respectively. Dynamic response times of all fabricated sensors were found to be less than 30 s (c) 2022 Elsevier B.V. All rights reserved.
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    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 Salih
    In 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.
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    Effect of Cobalt Doping on Nanostructured CuO Thin Films
    (Springer, 2014) Bayansal, Fatih; Taskopru, Turan; Sahin, Bunyamin; Cetinkara, Haci Ali
    The growth of cobalt-doped nanostructured CuO thin films using the successive ionic layer adsorption and reaction (SILAR) method is presented. It is found that Co doping considerably influences the structural (X-ray diffraction (XRD)), morphological (finite-element-scanning electron microscopy (FESEM)), and optical (ultraviolet/visible (UV/vis.) and Raman) properties of the films. XRD experiments evidence that the crystallite size of the films decreased with increasing Co doping. FESEM images reveal that the grain size of the nanostructures decreased with increasing doping concentration. By UV/vis. analysis, it is found that Co doping has a decreasing effect on band gap energy. The broadening and downshift of the Raman peaks are mainly attributed to the quantum confinement effect of CuO nanostructures.
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    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 Ali
    Mn0.2Ni0.8Fe2O4 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.