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Öğe Biocompatible multi-walled carbon nanotube-CdTe quantum dot-polymer hybrids for medical applications(ELSEVIER SCIENCE BV, 2015) Başlak, Canan; Kars, Meltem Demirel; Karaman, Mustafa; Kuş, Mahmut; Çengeloğlu, Yunus; Ersöz, MustafaHerein we report the synthesis of polymer coated quantum dots (QDs)-carbon nanotube composite material with high biocompatibility and low cellular toxicity. The synthesized multi-walled carbon nanotube (MWCNT)-QD-(-poly(glycidyl methacrylate)) (pGMA) hybrids were characterized using X-ray photoelectron spectroscopy, laser scanning confocal microscopy, transmission electron microscopy and scanning electron microscopy. The results showed that quantum dots were well-distributed on nanotube surfaces in high density. The toxicological assessments of QDs and MWCNT-QD-polymer hybrids in human mammary carcinoma cells and their fluorescence imaging in living cell system were carried out. MWCNT-QD-polymer hybrids possess intense red fluorescence signal under confocal microscopy and good fluorescence stability over 6-h exposure in living cell system. The toxicity comparison of QDs and MWCNT-QD-polymer hybrids has shown that the existence of PGMA thin coating on MWCNT-QD hybrid surface decreased the cellular toxicity and increased biocompatibility. (C) 2014 Elsevier B.V. All rights reserved.Öğe Colloidal CuZnSnSe4-xSx nanocrystals for hybrid solar cells(ELSEVIER, 2015) Kuş, Mahmut; Özel, Faruk; Büyükçelebi, Sümeyra; Aljabour, Abdalaziz; Erdoğan, Ayşenur; Ersöz, Mustafa; Sarıçiftçi, Niyazi SerdarWe report the synthesis of different colloidal CZTSe(4-x)S(x) nanocrystals and their performance in [6,6]-phenyl C61 butyric acid methyl ester (PCBM) based organic/inorganic hybrid bulk heterojunction solar cells. Synthesis of colloidal CuZnSnSe4-xSx were performed and characterized by XRD, TEM, SEM, UV-Visible absorption techniques. Electrochemical and photovoltaic properties were investigated. The best device concept, ITO/PEDOT:PSS/CZTS:PCBM blend (1:10)/Al, showed 280 mu A/cm(2) short circuit current, I-sc with 300 mV open circuit voltage V-oc, and fill factor FF of 0.38. (C) 2014 Elsevier B.V. All rights reserved.Öğe A comparative study on fabrication of Cu2ZnSnS4 (CZTS) nanofibers using acetate and chloride metal precursors(SCIENTIFIC TECHNICAL RESEARCH COUNCIL TURKEY-TUBITAK, 2015) Büyükbekar, Burak Zafer; Özel, Faruk; Şakalak, Hüseyin; Çavuşoğlu, Halit; Ersöz, Mustafa; Kuş, Mahmut; Yavuz, Mustafa SelmanThis study reports, for the first time, the fabrication of electrospun Cu2ZnSnS4 (CZTS) nanofibers using metal acetate precursors. Viscous poly(vinyl pyrrolidone) (PVP) solution containing acetate or chloride salts of copper, zinc, and tin was electrospun onto a conductive substrate. The PVP nanofibers that have a mixture of metal salts were annealed at elevated temperatures. After calcination, these nanofibers were treated with the sulfur source and then annealed again in order to generate CZTS nanofibers. The CZTS nanofibers generated from acetate and chloride salts were characterized and compared. Belt-like and wire-like nanofibers were obtained when using metal acetate and chloride precursors, respectively.Öğe A comparative study on fluorescence quenching of CdTe nanocrystals with a serial of polycyclic aromatic hydrocarbons(ELSEVIER SCIENCE BV, 2014) Başlak, Canan; Kuş, Mahmut; Çengeloğlu, Yunus; Ersöz, MustafaWe report sensing different polycyclic aromatic hydrocarbons (PAHs) with colloidal CdTe nanocrystals. The effect of molecular structure on quenching rate for 2-hyroxy-1-naphthaldehyde (2H-1N), 9,10-phenanthraquinone (PQ), 9-anthracenecarboxaldehyde (9-AC) and quinoline (Q) is presented. The quenching rate constants are observed to be strongly dependent on the molecular structure. PQ consisting of two carbonyl groups, shows the highest rate constant while Q shows the worst one. Both static and dynamic quenching are simultaneously observed for PQ and 2H-1N. Therefore extended Stern-Volmer equations are used to calculate rate constants. Results showed that dynamic quenching is a dominant process. The rate constants for PQ 2H-1N, 9-AC and Q are calculated to be 64.84, 10.73, 10.66 and 1.85 respectively. (C) 2014 Elsevier B.V. All rights reserved.Öğe Effect of doping on thin film solar cell efficiency based on ZnMn2O4 nanocrystals(ELSEVIER, 2019) Sarılmaz, Adem; Özel, Faruk; Aljabour, Abdalaziz; Khaskheli, Abdul Rauf; Kuş, MahmutThe present study reports, for the first time, a facile synthesis for ternary ZnMn2O4 nanocrystals synthesized by a simple and low cost two-phase method. Those nanocrystals were used on thin film solar cell as active absorber layer. The resulting nanocrystals were characterized by XRD, TEM, AFM-MFM, FTIR and JV characterization techniques to investigate the crystalline behavior, chemical composition, morphology and optical properties. Two phase method allows the successful synthesis of oleic acid (OA) capped ZnMn2O4 nanocrystals with 5-10 nm particle size. After doping of the ZnMn2O4 nanocrystals at different ratios with P3HT:PCBM, an enhancement was observed in the solar cell performances based on thin films. The power conversion efficiency of P3HT:PCBM-ZnMn2O4 thin film solar cell was investigated by J-V characteristic curve and as a result of this study, the highest efficiency was achieved as 3.27% with a doping ratio of 1%. Thus we believe that this work will open a new perspective to the synthesis of ZnMn2O4 materials for applications in the field of energy conversion systems. (C) 2019 Elsevier Ltd. All rights reserved.Öğe Electrospun Nanofibers Prepared with CdTe QDs, CdTeSe QDs and CdTe/CdS Core-Shell QDs(2018) Başlak, Canan; Köysüren, Özcan; Kuş, MahmutIn this study, a novel method is used to prepare water-soluble CdTe, CdTeSe quantum dots (QDS) and CdTe/CdS core-shell QDs by using Te, Se, NaBH4, and CdCl2 as precursors. Electrospinning method is used to obtain polyvinyl alcohol (PVA)/QDs composite nanofibers. A series of PVA/QDs nanofiber mats with three different QDs content are prepared. Transmission electron microscopy (TEM) and X-ray powder diffraction (XRD) have been used to characterize QD nanoparticles. In addition, for characterization of the composite nanofibers, scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used. QDs have a good dispersed crystalline structure with an average crystalline size between 2-4 nm. Morphology analyses reveal that the composite nanofibers with an average diameter ranging from 50 to 250 nm are prepared using the electrospinning technique.Öğe Enhanced uptake capacities and isosteric heats of CO2 and CH4 adsorption on spent coffee ground activated carbons loaded with metal ions(SCIENTIFIC TECHNICAL RESEARCH COUNCIL TURKEY-TUBITAK, 2019) Kırbıyık, Çisem; Büyükbekar, Burak Zafer; Kuş, Mahmut; Ersöz, MustafaLow-cost activated carbon (AC) samples obtained from waste coffee grounds were used for CO2 and CH4 adsorption. ACs were prepared by chemical activation and carbonized at three different temperatures. AC carbonized at 800 degrees C showed a relatively high surface area (582.92 m(2) g(-1)) and high adsorption capacities of 2.6 mmol g(-1) and 1.1 mmol g(-1) at 25 degrees C for CO2 and CH4, respectively. Adsorbent samples were prepared by loading of Fe3+ metal ions onto ACs and their adsorption capacities were compared with those of nonloaded ACs. As expected, the loading of Fe3+ metal ions increased the adsorption capacities at all temperatures and the adsorption capacity of Fe3+-loaded AC carbonized at 800 degrees C was 3.1 mmol g(-1) for CO2 and 1.2 mmol g(-1) for CH4 at 25 degrees C. The isosteric heats of adsorption were calculated at 0-35 degrees C with the range of 20-35 kJ mol(-1) and 18-23 kJ mol(-1) for CO2 and CH4, respectively. According to our findings, bio-based ACs can be used as an effective and alternative adsorbent for capturing different gas molecules.Öğe Humidity Adsorption Kinetics of Calix[4]arene Derivatives Measured Using QCM Technique(Elsevier, 2010) Okur, Salih; Kuş, Mahmut; Özel, Faruk; Aybek, Vildan; Yılmaz, MustafaThis study focuses on the characterization of sulphonated calix[4]arene derivative films coated on a quartz substrate with a thickness of 40 nm by spin coating method for humidity detection. The humidity adsorption kinetics of the sulphonated calix[4]arene films was investigated by quartz crystal microbalance (QCM) technique. The Langmuir model was used to determine the adsorption rates and Gibbs free energy for various relative humidities between 11% and 97%. Our reproducible experimental results show that suphonated calix[4]arene films have a great potential for humidity sensing applications at room temperature operations.Öğe Humidity Adsorption Kinetics of Water Soluble Calix[4]arene Derivatives Measured Using QCM Technique(Elsevier Science Sa, 2010) Okur, Salih; Kuş, Mahmut; Özel, Faruk; Yılmaz, MustafaWe report on the optimization and characterization of water soluble calix[4]arene derivative as a humidity sensor based on quartz crystal microbalance technique. The moisture adsorption and desorption kinetics of calix[4]arene were investigated. The Langmuir model was used to determine the kinetic parameters such as adsorption. desorption rates and Gibbs free energy between relative humidity between 29% and 78%. Reproducible experimental results were obtained showing that water soluble calix[4]arene films have a great potential for humidity sensing applications at room temperature operations.Öğe Improvement in electrical performance of half-metallic Fe3O4/GaAs structures using pyrolyzed polymer film as buffer layer(TAYLOR & FRANCIS LTD, 2014) Akın, Seçkin; Özel, Faruk; Kuş, Mahmut; Sönmezoğlu, SavaşIn this work, the Fe3O4 magnetic nanoparticles (MNPs) were synthesized by a colloidal method. TEM images reveal that Fe3O4 MNPs are spherical in shape with a narrow size distribution in the range of 6-7 nm. These MNPs were used in the fabrication of two types of n-GaAs-based structures: (i) Fe3O4/n-GaAs (reference); and (ii) Fe3O4/PPF/n-GaAs. We present that carbon-based pyrolyzed polymer films (PPFs), as a buffer layer, can control the electrical characteristics of a conventional Fe3O4/n-GaAs device. The behaviour of the apparent barrier height and ideality factor with the interfacial layer due to the presence of the interface state density is discussed. PPF raises the barrier height in a Fe3O4/PPF/n-GaAs half-metallic/insulator/semiconductor (h-MIS) device as high as 0.62 +/- 0.002 eV. Furthermore, Fe3O4/PPF interfaces exhibit unique electronic properties including high-quality interface, low series resistance (from 17.73 k Omega to 85.66 Omega) and extremely low interface state density (1.76 x 10(12) eV(-1) cm(-2)). Compared to the electrical performance for the Fe3O4/n-GaAs junction, that for the Fe3O4/PPF/n-GaAs junction was enhanced.Öğe Inhibition effects of different toothpastes on demineralisation of incipient enamel lesions(QUINTESSENCE PUBLISHING CO INC, 2019) Altan, Halenur; Göztaş, Zeynep; Kahraman, Kamil; Kuş, Mahmut; Tosun, GülPurpose: To evaluate the inhibitory effects of different toothpastes on demineralisation of incipient enamel lesions using a toothbrush simulator. Materials and Methods: Fifty enamel specimens were prepared from extracted human molars. The specimens were randomly assigned to the following groups (n = 10/group): 1. no treatment (control); 2. toothpaste containing arginine (ProRelief, Colgate;); 3. fluoride toothpaste (Pronamel, Sensodyne GlaxoSmithKlein); 4. tooth mousse containing casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) (Recaldent, GC); 5. toothpaste (Restore, Dr. Collins) containing bioactive glass (NovaMin, GlaxoSmithKlein). All specimens were exposed to pH cycling. The remineralising agents were applied to the samples with a toothbrush simulator for 2 min twice a day for five days. The weight percentage of mineral changes for the elements calcium (Ca), phosphorus (P), sodium (Na) and silica (Si) were measured by SEM energy-dispersive x-ray spectroscopy (SEM-EDX). SEM revealed properties of treated enamel surfaces. The data were analysed using one-way ANOVA. Results: Statistically significantly higher levels of Ca and P were found in all groups compared to the control (p < 0.05). Conclusions: The toothpastes' efficacy of inhibiting demineralisation depended on the active ingredients in the respective toothpaste. The demineralisation inhibition efficacy of the tested toothpastes depended on the active ingredients in the toothpaste.Öğe Interface modification of DNTT-based organic field effect transistors using boronic acid derivatives(Institute of Physics Publishing, 2020) Alıç, Tuğbahan Yılmaz; Ablat, Abduleziz; Kyndiah, Adrica; Nicolas, Yohann; Can, Mustafa; Kuş, Mahmut; Abbas, MamatiminThe dielectric/semiconductor interface in organic field effect transistors (OFETs) is critical to their performance. Modification of this interface with functional molecules provides a wide range of possibilities for their applications as sensors. In this work, boronic acid molecules were used to modify the SiO2 dielectric surface in dinaphtho[2,3-b:2?,3?-f]thieno[3,2-b]thiophene based OFETs. The device parameters, including most notably the threshold voltage, were significantly improved. The dielectric/semiconductor interface was analyzed using various measurement techniques, such as contact angle and atomic force microscopy. Our work provides evidence that easily functionable boronic acid derivatives improve the device performance of OFETs, which lays the foundation for further studies of such interface modified OFETs for use in sensing applications. © 2019 IOP Publishing Ltd.Öğe LUMINESCENCE ENHANCEMENT OF OLED PERFORMANCE BY DOPING COLLOIDAL MAGNETIC Fe3O4 NANOPARTICLES(EMW PUBLISHING, 2013) Kuş, Mahmut; Özel, Faruk; Varal, Nurhan M.; Ersöz, MustafaWe report synthesis of magnetic Fe3O4 nanoparticles (MNPs) based on two phase method and their application in organic light-emitting devices (OLEDs) as blend with emissive Polyfluorene (PFO) matrix. Two phase method allows to successively synthesizing oleic acid capped MPNs with 5-10 nm particle size. Colloidal MNPs can be easily mixed with emissive polymer solutions to obtain a blend for OLED application. The electroluminescence efficiency increases by doping with MNPs into emissive layer. Different dopant concentrations varied from 0,4% to 2% were monitored. It was observed that the electroluminescence increases up to 1% w/v doping ratio. The luminance of OLEDs increased from 15.000 cd/m(2) to 24.000 cd/m(2) in comparison pristine device with 1% MNP doped device.Öğe Microwave Assisted Synthesis of Chitosan Nanoparticles(TAYLOR & FRANCIS INC, 2011) Koçak, Nuriye; Şahin, Mustafa; Akın, İlker; Kuş, Mahmut; Yılmaz, MustafaChitosan nanoparticles (CHN) were prepared based on ionotropic gelation between low moleculer weight chitosan and sodium tripolyphosphate (TPP) under microwave irradiation. Particle size, zeta potential, and FT-IR techniques were used for characterization of CHN. The influence of reaction time on the nanoparticle size distribution was investigated, and the results showed that the microwave irradiation method evidently decreases the reaction times and particle size over the conventional method. It was determined by the results of the zeta potential measurements that synthesized CHN under microwave irradiation clearly exhibits more homogeneous and stable dispersion.Öğe A multifunctional ınterlayer for solution processed high performance ındium oxide transistors(NATURE PUBLISHING GROUP, 2018) Kyndiah, Adrica; Ablat, Abduleziz; Guyot-Reeb, Seymour; Schultz, Thorsten; Zu, Fengshuo; Koch, Norbert; Amsalem, Patrick; Chiodini, Stefano; Alıç, Tuğbahan Yılmaz; Topal, Yasemin; Kuş, Mahmut; Hirsch, Lionel; Fasquel, Sophie; Abbas, MamatiminMultiple functionality of tungsten polyoxometalate (POM) has been achieved applying it as interfacial layer for solution processed high performance In2O3 thin film transistors, which results in overall improvement of device performance. This approach not only reduces off-current of the device by more than two orders of magnitude, but also leads to a threshold voltage reduction, as well as significantly enhances the mobility through facilitated charge injection from the electrode to the active layer. Such a mechanism has been elucidated through morphological and spectroscopic studies.Öğe Photocatalytic hydrogen evolution based on Cu2ZnSnS4, Cu2ZnSnSe4 and Cu2ZnSnSe4-xSx nanofibers(ROYAL SOC CHEMISTRY, 2015) Gonce, Mehmet K.; Doğru, Melike; Aslan, Emre; Özel, Faruk; Patır, İmren Hatay; Kuş, Mahmut; Ersöz, MustafaNew photocatalytic systems for hydrogen evolution from water have been reported by using low cost and environmentally-friendly Cu-2-ZnSnS4, Cu2ZnSnSe4, and Cu2ZnSnSe4-xSx nanofiber catalysts in the presence of eosin Y as a photosensitizer and a sacrificial reducing agent triethanolamine under visible light irradiation. The rate of hydrogen evolution with Cu2ZnSnS4 is greater than those with Cu(2)znSnSe(4) and Cu2ZnSnSe4-xSx, producing hydrogen at 1428 mu mol g(-1) h(-1), 833 mu mol g (1) h(1) and 739 mmol g(1) h(1), respectively.Öğe Solution processed white light photodetector based N, N '-di(2-ethylhexyl)-3,4,9,10-perylene diimide thin film phototransistor(ELSEVIER SCIENCE SA, 2014) Tozlu, Cem; Kuş, Mahmut; Can, Mustafa; Ersöz, MustafaIn this study, a solution-processed n-type photo-sensing organic thin film transistor was investigated using polymeric dielectric under different white light illuminations. N, N'-di (2-ethylhexyl)-3,4,9,10-perylene diimide and divinyl tetramethyl disiloxane-bis (benzo-cyclobutene) were used as a soluble active organic semiconductor and as a dielectric material, respectively. Stable amplification was observed in the visible region without gate bias by the device. The electrical characterization results showed that an n-type phototransistor with a saturated electron mobility of 0.6 x 10(-3) cm(2)/V.s and a threshold voltage of 1.8 V was obtained. The charge carrier density of the channel of the device exhibited photo-induced behaviors that strongly affected the electrical properties of the transistor. The photosensitivity and photoresponsivity values of the device were 63.82 and 24 mA/W, respectively. These findings indicate that perylene diimide is a promising material for use on organic based phototransistors. (C) 2014 Elsevier B.V. All rights reserved.Öğe The synthesis of 4,4-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(N,N-diphenylaniline) organic semiconductor and use of it as an interlayer on Au/n-Si diode(SPRINGER, 2019) Yıldırım, Murat; Erdoğan, Ayşenur; Yüksel, Ömer Faruk; Kuş, Mahmut; Can, Mustafa; Akın, Ü.; Tuğluoğlu, NihatIn the present study, firstly, a 4,4-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(N,N-diphenylaniline) (FC) organic compound was synthesized and its structural and optical characterization were carried. Then, the effect on the device of the FC thin film prepared between n-type silicon substrate and gold metal by the spin coating technique was reported. The ideality factor (n), barrier height (phi B) and series resistance (Rs) values of the prepared structure from the I-V data have been found at 1.08, 0.78eV and 240 at room temperature (300K), respectively. According to the Gaussian distribution of the barrier height obtained from the various temperature ranges (220-380K), the phi b0 and A* values from the ordinate intercept and the slope of the modified Richardson curve of ln versus 1/T plot which has been found to be 0.97eV and 114 A/cm(2)K(2), respectively. Results indicate that the high barrier height is achieved for the Au/FC/n-Si metal-organic layer-semiconductor diode as compared to the Au/n-Si metal-semiconductor (MS) diode.
