Yazar "Demir, Ahmet" seçeneğine göre listele
Listeleniyor 1 - 20 / 32
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Boosting inverted type organic solar cell efficiency through the use of spray coated Y and Sn co-doped zinc oxide nanoparticles as an electron transport layers(Springer, 2023) Gegin, Keziban; Demir, Ahmet; Ozturk, Sadullah; Erkovan, Mustafa; Kosemen, ArifThe purpose of this study was to investigate the use of zinc oxide nanoparticles (ZnO NPs) as an electron transport layer (ETL) in inverted type organic solar cells (IOSCs). Three different forms of ZnO NPs were synthesized: undoped, doped with Sn or Y, and co-doped with combinations of these elements (Sn-co-doped Y). The ZnO NPs ETL was introduced into the solar cells using a spray coating technique, resulting in a bulk heterojunction structure of ZnO NPs/P3HT:PCBM/V2O5/Ag. Various methodological approaches were used to characterize the ZnO nanoparticles, including scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and ultraviolet/visible spectrophotometer. The current-voltage performance of the solar cells was measured under 100 mW/cm(2) white light. The results showed that the efficiency of the solar cells using undoped ZnO as ETL was 3.09%. However, the use of 0.5 wt% Sn and 1 wt% Y co-doped ZnO as ETL significantly improved the efficiency to 3.67%, representing an approximate increase of 19% compared to the undoped ETL. All experimental processes were performed under ambient air conditions. In conclusion, this study highlights the potential of using doped or co-doped ZnO NPs as ETL for fabricating IOSCs at low temperatures and improving their efficiency.Öğe Channel Length Modulation in a Polystyrene Insulated Organic Field Effect Transistor Using PEDOT: PSS Composite Electrode(2018) Demir, AhmetChannel length-modulated Organic Field Effect Transistor (OFET) was fabricated on a prepatterned sourcedrainIndium Tin Oxide (ITO) substrate by spin coating method using a Poly (3-hexylthiophene-2,5-diyl)(P3HT) semiconductor and Polystyrene (PS) insulator. Poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was used as the gate electrode. Thus, the structure of the OFET devicewas obtained as ITO/P3HT/PS/PEDOT:PSS. ITO/PS/PEDOT:PSS structure was prepared using the samemethod for measuring the capacitance of the polymer insulator. Output and transfer current-voltage (I-V)characteristics of the electrical characterization of the obtained OFET devices were obtained in full darknessand in the air environment. Basic parameters of OFET devices; voltage threshold (VTh), field effect mobility(FET) and the current on/off ratio (Ion/off) are exracted from the capacitance-frequency (C-f) graph of theITO/PS/PEDOT:PSS structure. Produced PS-OFETs have been found to exhibit good device performance,such as low VTh, acceptable mobility and Ion/off values.Öğe Comparative investigation of electronic parameters of low voltage organic field-effect transistors with variable capacitance non-ionic gel gate dielectrics(Elsevier, 2019) Yardım, Tayfun; Yücedağ, İbrahim; Allı, Sema; Allı, Abdulkadir; Demir, Ahmet; Kösemen, ArifNon-ionic gel dielectrics (NIGDs) have high effective capacitances (C-EFF) which can be used to reduce the operating voltage of the organic field-effect transistors (OFETs). Limited work has been carried out about these kinds of dielectrics although they have advantages of low cost and easy production. Besides, by mixing propylene carbonate (PC) with various kinds of polymers in order to tune the C-EFF of the blend, electronic parameter performance of the OFETs can be improved. In this study, regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT) based OFETs were fabricated. Specifying the poly(methyl-acrylate) (PMA) as a reference dielectric and adjusting the soybean oil to methyl acrylate weight ratio in the polymerization process to form copolymers of PMA, totally three types of dielectrics were synthesized and transformed into a gel state to obtain the reduced C-EFF. Gel dielectrics were named according to the soybean oil to methyl acrylate weight ratio. Such that, %0 ratio stands for NIGDO, %8 ratio stands for NIGD1 and %11 ratio stands for NIGD2 and OFETs fabricated with these NIGDs were named with regard to these names (NIGOFET0, NIGOFET1, and NIGOFET2). After the electrical characterization, it was seen that mobility enhanced as the C-EFF decreased as predicted. It could be attributed to a formation of less self-localization of the charge carriers in the semiconductor-dielectric interface. Moreover, it was seen that NIGOFET1 had the lowest Subthreshold Swing (SS) and off-current (I-OFF) consequently the highest on-to-off current ratio (I-ON/I-OFF). It implied that it had better insulation property and semiconductor-dielectric interface compared to the other NIGOFETs.Öğe The comparative investigation on synthesis, characterizations of silver ion-imprinting and non-imprinting cryogels, their impedance spectroscopies and relaxation mechanisms(Springer, 2019) Şarkaya, Koray; Demir, AhmetIn the present study, a novel ion-imprinting and non-imprinting cryogel samples have been prepared using ion-imprinting technique and the dielectric properties have been investigated using an impedance spectroscopy method. In the preparation of ion-imprinted cryogel, at the first attempt, N-methacryloly-(l)-cysteine methyl ester was used as the metal complexing monomer. Ag+-imprinted poly(hydroxyethyl methacrylate-N-methacryloly-(l)-cysteine methyl ester) cryogel was produced by bulk polymerization. Poly(2-hydroxyethyl methacrylate) was selected as the basic matrix by considering properties, high chemical and mechanical stability. After removal of template (silver ions), the ion-imprinted cryogel was used for the removal of photo-film-containing materials. The dielectric properties of cryogel samples have also been investigated by impedance spectroscopy within the frequency range of 1 Hz-10 MHz. The real part of the permittivity increases at low frequencies as electrode effects become dominant. It shows a constant value at high frequencies due to dipole polarization. On the other hand, the imaginary part does not show a relaxation peak as the relaxation time of samples is very short. The frequency dependence of electrical modulus has also been investigated. The real part of electrical modulus (M ' (f)) is an indicative of negligible electrode polarization phenomenon in the test material. The behavior of the imaginary part of frequency dependent electrical modulus (M '' (f)) exhibit that the dielectric relaxation process is usually not frequency-activated state. Dielectric relaxation process occurs spontaneously due to the hopping mechanism of charge carriers.Öğe A Comparative Study on the Main Electrical Parameters of Au/n-Si, Au/Biphenyl-CuPc/n-Si/ and Au/Biphenylsubs-CoPc/n-Si/ Type Schottky Barrier Diodes(Amer Scientific Publishers, 2016) Demir, Ahmet; Yücedağ, İbrahim; Ersöz, Gülçin; Altındal, Şemsettin; Baraz, Nalan; Kandaz, MehmetWe have produced Au/n-Si (MS), Au/n-Si/biphenyl-CuPc (MPS1), and Au/n-Si/biphenylSubs-CoPc (MPS2) type Schottky barrier diodes (SBDs) to investigate the effect of interfacial layer on the main electrical parameters. Biphenyl-CuPc and biphenylSubs-CoPc interfacial layers were successfully coated on n-Si substrate by using the spin coating system. The current-voltage (I-V) characteristics of these structures were investigated at room temperature and they were considerably influenced by the interfacial layer. The main electronic parameters of these three type diodes that are reverse saturation current (I-0), series resistance (R-s), ideality factor (n), and zero-bias barrier height (Phi(B0)) were determined from the forward bias I-V characteristic. The energy density distribution profile of the interface states (N-ss) was also obtained from the forward I-V data by taking into account voltage dependent effective barrier height (Phi(theta)) and ideality factor n(V), and increased from the bottom of conductance band to the mid-gap energy of Si almost exponentially. In addition, the voltage dependent profile of resistance was obtained from capacitance-voltage (C-V) and conductance-voltage (G/omega - V) data at high frequency (500 kHz) at room temperature for each diode. Experimental results show that the R-s, N-ss and the interfacial layer are significantly effective on the electrical characteristics.Öğe Comparison of Electronic Parameters of Low Voltage Organic Field-Effect Transistors with Novel Gel Gate Insulators(Amer Scientific Publishers, 2019) Yardım, Tayfun; Demir, Ahmet; Allı, Sema; Allı, Abdulkadir; Kösemen, Arif; Yücedağ, İbrahimIn this paper, regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT)-based low voltage organic field-effect transistors (OFETs) with three kinds of non-ionic gel gate insulators (NIGIs) were fabricated and compared in terms of their electronic properties. One of the NIGI was prepared by mixing solution-processed poly(methyl acrylate) (PMA) with propylene carbonate (PC) until it becoming a gel state and same procedure was applied to the solution-processed copolymers of PMA called as P18 and P28. As a result, it was seen that fabricated OFETs could be operated at low voltages which is very significant property in order to manipulate the devices in low power electronic applications. On the other hand, it was noted that mobilities of the transistors were enhanced by reducing the effective capacitance (EC) of the NIGIs. This could be attributed to less charge carrier self-localization formation between the insulator-semiconductor interface when the EC was decreased. Furthermore, devices showed similar on-to-off current (I-ON/I-OFF) ratio which was good for using them in inverter applications. Besides, subthreshold swing (SS) for the P18 non-ionic gel OFET (NIGOFET) was the highest probably due to the less water-repellent chemical structure of the P18 NIGI.Öğe Controlling the electrical characteristics of Au/n-Si structure with and without (biphenyl-CoPc) and (OHSubs-ZnPc) interfacial layers at room temperature(Wiley, 2017) Baraz, Nalan; Yücedağ, İbrahim; Demir, Ahmet; Demir, Gülçin Ersöz; Altındal, Şemsettin; Kandaz, MehmetIn order to interpret well whether or not the organic or polymer interfacial layer is effective on performance of the conventional Au/n-Si (metal semiconductor [MS]) type Schottky barrier diodes (SBDs), in respect to ideality factor (n), leakage current, rectifying rate (RR), series and shunt resistances (R-s, R-sh) and surface states (N-ss) at room temperature, both Au/biphenyl-CoPc/n-Si (MPS1) and Au/OHSubs-ZnPc/n-Si (MPS2) type SBDs were fabricated. The electrical characteristics of these devices have been investigated and compared by using forward and reverse bias current-voltage (I-V) characteristics in the voltage range of (-4V)-(4V) for with and without (biphenyl-CoPc) and (OHSubs-ZnPc) interfacial layers at room temperature. The main electrical parameters of these diodes such as reverse saturation current (I-0), ideality factor (n), zero-bias barrier height (phi(B0)), RR, R-s and R-sh were found as 1.14x10(-5)A, 5.8, 0.6eV, 362, 44 and 15.9k for reference sample (MS), 7.05x10(-10)A, 3.8, 0.84eV, 2360, 115 and 270k for MPS1 and 2.16x10(-7)A, 4.8, 0.7eV, 3903, 62 and 242k for MPS2, respectively. It is clear that all of these parameters considerably change by using an organic interfacial layer. The energy density distribution profile of N-ss was found for each sample by taking into account the voltage dependence of effective barrier height (phi(e)) and ideality factor, and they were compared. Experimental results confirmed that the use of biphenyl-CoPc and OHSubs-ZnPc interfacial layer has led to an important increase in the performance of the conventional of MS type SBD. Copyright (c) 2015 John Wiley & Sons, Ltd.Öğe Current conduction in Schottky barrier diodes with poly(propylene glycol)-b-polystyrene block copolymer interfacial layer(Natl Inst Science Communication-Niscair, 2017) Yıldırım, Mert; Allı, Abdulkadir; Demir, Ahmet; Allı, Sema; Gökçen, MuharremPolymeric materials have gained great importance in electron devices. There has been considerable number of studies on block copolymers due to enhanced features that appear after co-polymerization. In this study, poly (propylene glycol)-b polystyrene block copolymer has been synthesized and Schottky bather diodes (SBDs) have been fabricated with this block copolymer. Current-voltage (I-V) measurements have been conducted at room temperature in order to investigate electrical characteristics and current conductions governing in these SBDs. Series resistance and shunt resistance of the SBDs have been calculated using Ohm's law. Ideality factor, reverse saturation current and zero-bias bather height of the SBDs have been extracted from the forward-bias I-V data. Fabricated SBDs exhibited high rectifying ratio of the order 10(4). Also, current conduction mechanisms and the density of interface states in the SBDs have been investigated. Calculated values of density of interface states in the SBDs are on the order of 10(13) which is acceptable for this kind of SBDs having polymeric interfacial layer.Öğe The effect of different rates of ultra-thin gossamer-like rGO coatings on photocatalytic performance in ZnO core-shell structures for optoelectronic applications(Elsevier Science Sa, 2022) Kırkbınar, Mine; Demir, Ahmet; Altındal, Şemsettin; Çalışkan, FatihIn the study, core-shell-structured Al/(ZnO:rGO)/pSi/Al photo-diodes were successfully fabricated using a sol-gel spin-coating method by varying the concentration of reduced-graphene oxide (rGO) from 1 % to 9 % (wt). The ZnO:rGO composite solution was coated on a silicon (p-Si) wafer at 1000 rpm and 300 K. Both aluminum back-ohmic and front-rectifier contacts were performed on the p-Si wafer by physical-vapor-deposition (PVD). The morphological and chemical structure of the photo-diodes were determined by using field-emission scanning electron microscopy (FE-SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD). The current -voltage (I-V) analysis in dark and under ultraviolet (UV, 365 nm) wavelength was utilized in detail. Basic electrical parameters, including the ideality factor (n), barrier height (BH) and series-shunt resistances (Rs, Rsh), were calculated using a variety of methods and compared to each other. The Card-Rhoderick method was used to extract energy-dependent profiles of interface traps (Nss). The core-shell-structured (ZnO-7 % rGO) photo-diode exhibited the best photocatalytic performance both in dark and under various illumination intensities (50-250 mW/cm2). The ZnO:rGO interlayer at the metal-semiconductor (M/S) interface leads to improvement of the photo-diode in respect of low-ideality factor/Nss/leakage-current and high-rectification and BH.Öğe Effect of inorganic salt solutions on consistency limits of kaolinite(2018) Varank, Gamze; Demir, Ahmet; Güvenç, Senem Yazıcı; Özçoban, Mehmet ŞükrüThis study presents the effect of different inorganic salt solutions (KCl, BaCl2, MgCl2, KNO3, Na2SO4 and MgSO4) at different concentrations on geotechnical properties (Atterberg Limits) of kaolinite material which can be used as impermeable bottom liner in barrier systems. Since the use of distilled water or tap water is far from being representative of the in-situ conditions in landfills, salt solutions were used to investigate the leachate effect on liner materials. Additionally, the mineralogical characterization of kaolinite was studied. Atterberg limits, specifically the liquid limit (LL) and plastic limit (PL) that were used for classifying the clayey soil samples according to the Unified Soil Classification System were determined whereas mineralogical studies performed included XRD, BET and FT-IR analyses. Results indicated that all salt solutions have a considerable effect on the consistency limits of kaolinite. The liquid limit values of kaolinite decreased with increasing chemical concentration whereas plastic limit values increased. It is observed that the effects of the divalent and trivalent cations on kaolinite were more apparent than those of monovalent cations. As a result chemical solutions decrease liquid limit values of high plasticity kaolinite materials, tend to reduce the thickness of the DDL and flocculate the kaolinite particles, resulting in reduction of swelling and increasing of hydraulic conductivity.Öğe Evaluation of Industrial Poly(tert-butyl acrylate) insulated A p-channel Organic Field-Effect Transistor (PtBA-p-OFET)(Duzce University, 2024) Demir, Ahmet; Musatat, Ahmad BadreddinPoly(tert-butyl acrylate) (PTB-p-A) has been investigated as a promising insulator layer for p-channel organic field effect transistors (p-OFETs) using the p-type semiconductor Poly(3-hexylthiophene-2,5-diyl (P3HT) due to its favorable insulating properties, good film-forming ability and electrical charge separation properties. Top-gate, bottom-contact PTBA-p-OFET devices are fabricated with Indium Thin Oxide (ITO) source/drain electrodes and a P3HT organic semiconductor layer. The frequency-dependent capacitance of the PTBA-p-OFETs was studied through a plot to determine the key parameters, including the threshold voltage (VTh), field-effect mobility (µFET), and the current on/off ratio (Ion/off) of the device. The PTB-p- OFETs exhibit field-effect mobility value of 6.13x10-4 (cm2/V.s), an on/off current ratio of 1.11x102, and a threshold voltage of -15.8 V. The capacitance-frequency characteristics of the capacitor structure were analyzed and found to have as 7.6 nF/cm2 per unit area. This work presents PTBA as a promising for high-performance p-OFET applications.Öğe Evaluation of novel thiophene branched polystyrene as insulator layer in organic electronic device(Elsevier Science Bv, 2019) Günaydın, Okan; Demir, Ahmet; Atahan, Alparslan; Yardım, Tayfun; Yücedağ, İbrahimA novel thiophene branched polystyrene copolymer (PS-Th) was successfully synthesized and well characterized. Two different Organic Field Effect Transistor (OFET) devices were fabricated by using this novel PS-Th material and polystyrene (PS) as insulator materials and main performance parameters of the devices such as mobility (mu(FET)), on/off ratio (I-on/off), and threshold voltage (V-Th) were compared. Consequently, our results indicated that PS-Th copolymer was efficiently working as dielectric material for OFETs. Moreover, mu(FET) significantly enhanced (approx. 3.7 times) compared to the PS based OFET device while V-Th and I-on/off were slightly increasing. This situation can be explained by well organized molecular arrangement at the dielectric-semiconductor interface via thiophene-thiophene interaction between semiconductor material Poly(3-hexylthiophene-2,5-diyl) (P3HT) and insulator material PS-Th chains. (C) 2019 Elsevier B.V. All rights reserved.Öğe Improvement of electric and photoelectric properties of the Al/n-ZnO/p-Si/Al photodiodes by green synthesis method using chamomille flower extract(Springer, 2023) Kırkbınar, Mine; İbrahimoğlu, Erhan; Demir, Ahmet; Çalışkan, Fatih; Altındal, ŞemsettinIn this study, zinc oxide nanoparticles (ZnO-NPs) were synthesized by green and chemically using the sol–gel method. They compared in terms of current–voltage (I–V) characteristics. The synthesized plant-based (ZnO-NPs) were characterized via Fourier-transform infrared-spectroscopy, X-ray diffraction (XRD), and field-emission scanning electron microscopy. The XRD analysis determined the existence of pure-crystalline of (ZnO-NPs). Particle size distribution was routinely employed to characterize the green synthesized powders for size distribution, and the reactivity of green synthesized particles was found smaller than chemically synthesized particles. The I–V measurements of prepared thin films characteristics were compared both in the dark and ultraviolet spectrum (365 nm) under 100 mW/cm2. While the reverse-saturation current (I0), ideality factor (n), and zero-bias barrier-height (?bo) values were extracted from the I–V data as 1.68 × 10–6 A, 2.43, 0.61 eV in dark and 7.27 × 10–5 A, 5.64, 0.50 eV under illumination for Al/(Bio-ZnO)/pSi and 7.99 × 10–6 A, 3.75, 0.57 eV in dark and 3.09 × 10–5 A, 5.71, 0.53 eV under illumination for Al/(Chemical-ZnO)/pSi photodiodes. These photodiodes' energy-dependent profiles were also obtained using the Card-Rhoderick method. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Öğe Influence of PVA and silica on chemical, thermo-mechanical and electrical properties of Celluclast-treated nanofibrillated cellulose composites(Elsevier Science Bv, 2017) Poyraz, Bayram; Tozluoğlu, Ayhan; Candan, Zeki; Demir, Ahmet; Yavuz, MustafaThis study reports on the effects of organic polyvinyl alcohol (PVA) and inorganic silica polymer on properties of Celluclast-treated nanofibrillated cellulose composites. Nanofibrillated cellulose was isolated from Eucalyptus camaldulensis and prior to high-pressure homogenizing was pretreated with Celluclast enzyme in order to lower energy consumption. Three nanocomposite films were fabricated via the casting process: nanofibrillated cellulose (CNF), nanocellulose-PVA (CNF-P)and,nanocellulose-silica (CNF-Si). Chemical characterization, crystallization and thermal stability were determined using FT-IR and TGA. Morphological alterations were monitored with SEM. The Young's and storage moduli of the nanocomposites were determined via a universal testing machine and DTMA. The real and imaginary parts of permittivity and electric modulus were evaluated using an impedance analyzer. The crystallinity values of the nanocomposites calculated from the FT-IR were in agreement with the TGA results, showing that the lowest crystallinity value was in the CNF-Si. The CNF-P displayed the highest tensile strength. At a high temperature interval, the storage modulus of the CNF-Si was greater than that of the CNF or CNF-P. The CNF-Si also exhibited a completed singular relaxation process, while the CNF and the CNF-P processes were uncompleted. Consequently, in terms of industrial applications, although the CNF-P composite had mechanical advantages, the CNF-Si composite displayed the best thermo-mechanical properties. (C) 2017 Elsevier B.V. All rights reserved.Öğe Investigating Magnetic, Dielectric, Optic And Morphologic Properties Of Nano-Nickel Oxide-Doped Ndfeo3(World Scientific Publ Co Pte Ltd, 2024) Zenkin, Kubra; Durmus, Sefa; Demir, AhmetIn this investigation, alpha-Fe2O3 was prepared via co-precipitation and nano-NiO and NdFeO3 were synthesized using the sol-gel method. For NdFe0.50.5Ni0.50.5O(3) synthesis, Nd(2)O3,alpha 3,-Fe2O3, and nano-NiO compounds were mixed via the solid state method. The effect of each component and that of nano-NiO on the NdFe0.50.5Ni0.50.5O(3) crystal properties was characterized by using X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), ultraviolet-visible (UV-Vis), vibrating sample magnetometer (VSM), impedance and bandgap analyses. The orthorhombic perovskite structure was confirmed by the XRD data. With the doping of nano-NiO, the unit cell volume was found to decrease. The UV-Vis spectroscopy showed that the nano-NiO-doped optical bandgap (E-g) had increased. The VSM analysis demonstrated that by doping nano-NiO to weak ferromagnetic NdFeO3, the resulting NdFe0.50.5Ni0.50.5O(3) was rendered superparamagnetic. The real and imaginary parts of dielectric permittivity (epsilon '' and epsilon '''') and the loss tangent (tan delta) characteristic of the compounds were measured at AC-signaled frequencies of 100 Hz-10 MHz and a voltage range of 0-20 V DC. The increase in active charge transmission with the doping of nano-NiO reduced the epsilon '' values. In addition, the large differences between the epsilon '' values were thought to be caused by the breakdown voltage (E-b) effect of the compounds. The epsilon '''' and tan delta changes revealed the dipole formation of the compounds at different voltages, their relaxation regions and their polarization mechanism type. The dielectric loss behavior of the compounds demonstrated their good dielectric material properties. This study investigated the effect of method difference and doped material particle size on magnetic and dielectric properties.Öğe Investigation of photo-induced change of electro-optical performance in a liquid crystal-organic field effect transistor (LC-OFET)(Taylor & Francis Ltd, 2016) Demir, Ahmet; Köysal, OğuzThis study aimed to improve the electrical characteristics of poly(3-hexylthiophene) (P3HT) and liquid crystal-organic field effect transistors (LC-OFETs) under UV illumination. Consequently, a novel LC-OFET was fabricated using a nematic liquid crystal (E63) and a P3HT mixture in an OFET cell. Cell thickness was determined through field emission scanning electron microscopy. For assessment of the electrical characteristics, the LC-OFET device was exposed to various UV light intensities in total darkness for the purpose of obtaining the output- and transfer-current voltage. The capacitance-frequency plot of the capacitor cell was then measured to determine the main parameters including the threshold voltage (V-Th), field effect mobility ((FET)) and current on/off ratio (I-on/off) of the device. Thus, the full characterisation and UV light response of the electronic parameters were determined for this new class of transistors. Results showed that the new LC-OFET exhibited good performance in the form of low V-Th, high(FET), and high I-on/off.Öğe Investigation of photoinduced change of dielectric and electrical properties of indium (III) phthalocyanine and fullerene doped nematic liquid crystal(Elsevier Science Sa, 2012) Özmen, Özge Tüzün; Gökşen, Kadir; Demir, Ahmet; Durmuş, Mahmut; Köysal, OğuzIn this work, we have studied photoinduced dielectric and electrical properties of E63 nematic liquid crystal (E63-LC) materials doped with indium (III) metallo phthalocyanine (In-MPc) and fullerene (C-60) in dark and under UV illumination. Doping concentration of In-MPc in E63-LC was chosen to be 5 wt%, whereas a trace amount of C-60 was used in investigated samples. Real and imaginary parts of dielectric permittivity were investigated in the frequency range of 100 Hz-10 MHz by using dielectric spectroscopy technique (DST). It was observed that doping agents and UV illumination enhanced the real part of dielectric permittivity at low frequencies, which was thought to originate from photoinduced charge transfer between In-MPc and C-60 caused by extra dipole strength in LC medium. In addition to that, critical frequency (f(c)) and relaxation time (tau) were obtained and analyzed for all investigated samples. Photoelectrical characteristics of hybrid LC structures were carried out by current voltage measurements. A major increase in electrical conductivity was observed in In-MPc and C-60 doped LC structures under UV irradiation. (C) 2012 Elsevier B.V. All rights reserved.Öğe Investigation of the dielectric and optic properties of rosehip seed extract loaded hydrogels(Elsevier B.V., 2023) Okutan, M.; Coşkun, R.; Yalçın, O.; Babuçoğlu, A. C.; Demir, AhmetRosehip seed (RS) extract-loaded hydrogel samples RS1 (poly(AMPS-co-MBAAm), RS2 (poly(AMPS- co - CrA- co - MBAAm)), RS3 (poly(AMPS - co - MAA - co - MBAAm)) and RS4 (poly(AMPS -co - IA - co- MBAAm)) were prepared to examine their structural and optical properties. Furthermore, frequency and bias voltage evolution of dielectric and electrical parameters were analyzed using impedance spectroscopy (IS) for all samples at room temperature (RT). Fluctuating and self-consistent results were obtained in the Ultraviolet–visible (UV) spectrum of the samples. The conductivity mechanisms were determined by calculating the s parameters of all samples for different regions. The complex impedance, capacitance, phase angles, dielectric constant, tangent factor, electric modulus, and frequency variation of ionic conductivity for the rosehip seed loaded hydrogel were successfully analyzed in detail using IS in the broadband frequency range. The increase in ionic conductivity of the RS-doped hydrogel with increasing frequency was attributed to its ability to exhibit the Langevin equivalent of Brownian motion in viscoelastic fluids, surface/bulk Maxwellian stress relaxation behavior, and the validity of the Stokes-Einstein relationship in biological fluids. In particular, the capacitive effect observed as a result of the Cole-Cole diagrams of the dielectric constant adapting to Smith Chat and the equivalent RC circuit allowed the material to be used as a capacitor. © 2022Öğe Investigation of the Performance of Poly(Methyl-Acrylate) as a Gate Dielectric in Organic Thin-Film Transistors(Springer, 2020) Yardim, Tayfun; Demir, Ahmet; Alli, Sema; Alli, Abdulkadir; Yucedag, IbrahimIn this study, we present two regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT)-based top-gate bottom-contact configured organic thin-film transistors (OTFTs) using poly(alpha-methyl acrylate) (PMA) and poly(methyl methacrylate) (PMMA) polymers separately as gate insulators for comparison. In order to compare only the performance of the dielectrics, the other parts of the devices were kept qualitatively and quantitatively identical. Unlike PMMA, PMA is flexible, and flexibility is a desirable property for an OTFT. Thus, utilizing PMA can be advantageous if it supports higher performance of the transistor. In this respect, the electronic parameters of the fabricated devices were extracted from transfer and output characteristics to determine the performance of PMA in OTFT applications. Results showed that the mobility of the OTFT with PMA (PMA-OTFT) was nearly three times greater than that of the OTFT with PMMA (PMMA-OTFT), while the PMA-OTFT threshold voltage (V-TH) was slightly less than that of the PMMA-OTFT, which was likely because of the greater effective capacitance (C-EFF) of the PMA layer compared to that of the PMMA layer. This is the main advantage of the PMA. On the other hand, the major downside is found in the reduced on-to-off current (I-ON/I-OFF) and increased subthreshold swing originating from a huge off-current (I-OFF), implying the existence of a large gate leakage current. Increasing the thickness of the PMA layer could reduce such large gate leakage current. However, this would lead to additional increase in the OTFT operating voltage. Therefore, further studies are required to improve the insulating property of the PMA polymer in order to substitute it for the PMMA.Öğe Life Cycle Assessment and Characterization of Tincal Ore Reinforced Polyester and Vinylester Composites(2023) Yılmaz, Emrah; Aydoğmuş, Ercan; Demir, AhmetIn this study, the quality performance, compressive strength, surface hardness, electrical conductivity, and life cycle assessment (LCA) of the composites produced by reinforcing tincal (Na2B4O7.10H2O) into polyester and vinylester resins at different rates have been determined. Tincal ore, which is ground with a particle size of 74-149 microns, is dried in an oven at 105 °C for 2 hours and then added to the resins at the ratios of 0 wt.%, 1 wt.%, 2 wt.%, and 3 wt.%. According to the results obtained, it has been determined that the compressive strength and Shore D hardness of the composite raises as the tincal mass ratio increases up to certain amounts. According to the mechanical test results, it is found that 3 wt.% tincal reinforcement maximized the compressive strength of the polyester composite, and 2 wt.% tincal reinforcement maximized the compressive strength of the vinylester composite. In the electrical conductivity test results, it is seen that the first relaxation time of the polyester composite is 2.14·10-4 s and the relaxation times of vinylester composite vary between 10-4 and 10-6 seconds. LCA results showed that vinylester composite had more environmental effects than polyester composite except for ozone layer depletion (ODP) effect. Although there is a partial increase (<0.5%) in the environmental impact of composites with tincal reinforcement, it is thought that the increase in the technical performance of the composites will tolerate this partial increase.
