Yazar "Demir, Ahmet" seçeneğine göre listele

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    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, Arif
    The 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.
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    Channel Length Modulation in a Polystyrene Insulated Organic Field Effect Transistor Using PEDOT: PSS Composite Electrode
    (2018) Demir, Ahmet
    Channel 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.
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    Channel Length Modulation in a Polystyrene Insulated Organic Field Effect Transistor Using PEDOT: PSS Composite Electrode
    (Sakarya University, 2018) Demir, Ahmet
    The Organic Field Effect Transistor (OFET) with channel length modulation was fabricated by spin coating method using a Poly(3-hexylthiophene) (P3HT) and the Polystyrene (PS) insulator on a prepatterned as source-drain Indium thin oxide (ITO) substrate. The poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was used as  gate electrode. So, the structure of OFET device is obtained as ITO/P3HT/PS/PEDOT:PSS. The ITO/PS/PEDOT:PSS structure was prepared using same method for capacitance measurements of a polymer insulator. Electrical characterization of OFET devices were held in total darkness and in air ambient for the purpose of achieving output and transfer current-voltage (I-V) characteristics. The main parameters such as the threshold voltage (VTh), field effect mobility (mFET) and current on/off ratio (Ion/off) of the OFET devices were extracted from capacitance-frequency (C-f) plot of the ITO/PS/PEDOT:PSS structure.  It was found that fabricated PS-OFETs exhibit good device performance such as low VTh, remarkable mobility, and  Ion/off values.
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    Cholesterol functionalized linear Poly(ε-caprolactone) polymers: Effects of chain length on mesomorphic and dielectric properties
    (Elsevier Science Sa, 2025) Doganci, Merve Dandan; Davarci, Derya; Uner, Melek; Demir, Ahmet; Musatat, Ahmad Badreddin; Akdogan, Mustafa; Doganci, Erdinc
    Cholesterol-functionalized linear poly (epsilon-caprolactone) (Chol-PCL) polymers with different chain lengths (n = 10, 20, 30, and 70) were successfully synthesized via a ring-opening polymerization reaction using cholesterol as initiator. Their structures were confirmed by 1H NMR and FT-IR spectroscopy, and their various dielectric properties were extensively investigated in a frequency range from 100 Hz to 1 MHz under different voltage conditions (0-20 V). The results revealed that all the obtained polymers have focal conic fan shape textures of the smectic phase, encouraging the mesomorphism. In particular, Chol-PCL30 showed superior dielectric performance and exhibited the highest capacitance values and optimal dielectric stability over the measured frequency spectrum. The study showed a non-linear relationship between the chain length of PCL and dielectric properties, with the medium chain length (n = 30) providing the most favorable molecular architecture for enhanced charge capability and dielectric response. Complex impedance analysis revealed a pronounced relaxation behavior as a function of chain length, with Chol-PCL30 showing the most pronounced impedance response. These results provide valuable insights into the structure-property relationships in cholesterol-modified PCL systems and their potential applications in dielectric materials. To address the limitations of existing dielectric materials and explore novel polymeric systems with enhanced electrical properties, cholesterol-functionalized linear poly (epsilon-caprolactone) (Chol-PCL) polymers were successfully synthesized with precisely controlled chain lengths (n = 10, 20, 30, and 70) via ring-opening polymerization using cholesterol as an initiator. Structural confirmation was achieved through 1H NMR and FT-IR spectroscopy. A comprehensive investigation into their dielectric properties, including capacitance, conductance, dielectric constant, dissipation factor, electrical modulus, and impedance, was conducted across a broad frequency range (100 Hz-1 MHz) under varying voltage conditions (0-20 V). All synthesized polymers exhibited focal conic fan shape textures characteristic of the smectic phase, indicating their mesomorphic nature. Notably, Chol-PCL30 demonstrated exceptional dielectric performance, exhibiting the highest capacitance values and notable dielectric stability across the measured frequency spectrum. This study revealed a significant non-linear correlation between the PCL chain length and the observed dielectric properties, with the medium chain length (n = 30) providing an optimal molecular architecture for enhanced charge storage capability and dielectric response. Furthermore, complex impedance analysis elucidated a pronounced relaxation behavior that was highly dependent on chain length, with Chol-PCL30 exhibiting the most significant impedance response. These findings offer crucial insights into the intricate structure-property relationships within cholesterol-modified PCL systems, paving the way for their potential application in advanced dielectric materials.
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    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, Arif
    Non-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.
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    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, Ahmet
    In 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.
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    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, Mehmet
    We 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.
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    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, İbrahim
    In 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.
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    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, Mehmet
    In 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.
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    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, Muharrem
    Polymeric 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.
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    Development of Sol-Gel Synthesized ZnO Nanoparticle-Incorporated Polymer-Based X-Ray Detectors: A Comparative Investigation of Device Architectures
    (Amer Chemical Soc, 2025) Selcuk, Nevin Nur; Ozturk, Sadullah; Kalkan, Yalcin; Demir, Ahmet; Gegin, Keziban; Kosemen, Arif
    The extensive use of X-rays in medical, security, and industrial applications has led to considerable interest in the development of advanced X-ray detection technologies. Conventional detectors based on inorganic semiconductors, such as silicon or germanium, face challenges, including high production costs and limited flexibility. This study investigates the potential of organic semiconductors, particularly ZnO nanoparticles (ZnO NPs) incorporated into a poly(3-hexylthiophene) (P3HT) matrix, for X-ray detection. The ZnO NPs, selected for their high mobility, large band gap, and thermal stability, were synthesized via a sol-gel method and integrated into P3HT to form composite layers at varying ratios (1:0.25, 1:0.5, and 1:0.75). Two different device architectures were fabricated: interdigitated (IDT) electrodes as resistive-based and diode-based devices with ITO/ZnO/P3HT/Graphite configurations. The influence of the ZnO NP concentration and device structure on X-ray detection performance was systematically investigated and evaluated. The results indicated that increasing the ZnO NP content enhanced electron transportation and improved the X-ray sensitivity of the devices. The ITO/ZnO/P3HT/Graphite device with a P3HT ratio of 1:0.75 exhibited the highest sensitivity (0.94 mu Gy/s) and the fastest response times, outperforming those of the IDT-based devices. This study demonstrates that organic semiconductors doped with ZnO NPs are promising candidates for cost-effective, flexible, and high-performance X-ray detectors.
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    The dielectric characteristics of spray deposited α-Si3N4:ZnO thin films: The nitride effect on frequency-dependent capacitance and conductance profiles
    (Elsevier, 2024) Ibrahimoglu, Erhan; Demir, Ahmet; Caliskan, Fatih; Tatli, Zafer
    The study focused on the effect of alpha-Si3N4 doping on the electrical/dielectric properties of ZnO thin films. Both alpha-Si3N4 doped and additive-free ZnO thin films were coated on p-Si substrates via a spray deposition method to achieve this. The electrical (current density (J)-voltage (V)) and dielectric properties (capacitance (C), conductance (G), dielectric loss (tan delta), reel/imaginary part of dielectric permittivity (epsilon ' and epsilon '') and electric modulus (M ' and M '')) were determined for all samples by using dielectric spectroscopy (DS) method. On the other hand, scanning electron microscopy (FESEM) and energy-dispersive spectroscopy (EDS) analysis were performed to evaluate microstructure, X-ray diffraction (XRD) was used to define chemical composition and atomic-force microscopy (AFM) analysis was carried out to characterise the topology of the coating layers. The thickness/surface roughness was obtained as similar to 82.5 nm/10.6 nm for undoped and- 99.5 nm/10.4 nm for nitride-doped samples, respectively. The maximum capacitance value (C) was obtained as 275 pF at -3.0V and 200 Hz, and the optimal conductance (G) value was also found as 45 mu S around 4.0V and 1 MHz in the nitride-doped sample. The average of alpha and tau values was calculated as 5.67 x 10(-5) s, 0.146 and 4.49 x 10(-5) s, 0.081 for nitride-doped and undoped ZnO, respectively. The increase in performance can be attributed to the homogeneous and almost equally-size distribution of the ZnO grain growth which is strongly controlled by alpha-Si3N4.
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    Dielectric property enhancement of glass fiber-reinforced concrete via TiO? nanocomposites
    (Elsevier, 2025) Ramazanoğlu, Doğu; Subaşı, Azime; Musatat, Ahmad Badreddin; Demir, Ahmet; Subaşı, Serkan; Maraşlı, Muhammed
    This study addresses the critical gap in traditional glass fiber-reinforced concrete (GFRC), which lacks tailored electrical properties for modern energy-related applications. We introduce a novel approach by incorporating a TiO?-based hybrid composite (TiO?-@) into GFRC to develop multifunctional composites with enhanced dielectric, mechanical, and energy storage capabilities. Experimental results demonstrate that TiO?-@ doping at 2 % concentration achieves the most significant improvements: a dielectric constant increase to ~420 at 100 Hz (compared to ~180 for undoped GFRC), capacitance enhancement to 71 pF at 100 Hz (versus 18 pF in the reference), and AC conductivity elevation by 205 % after aging. The 2 % TiO?-@ sample also exhibited a Leeb hardness increase to 486 HLD (from 159 HLD pre-aging), highlighting its structural robustness. Frequencydependent analyses revealed modified polarization mechanisms and charge transport dynamics, with ColeCole plots and impedance spectroscopy confirming reduced capacitive reactance and enhanced interfacial interactions. These results establish TiO?-@ as a transformative additive for GFRC, bridging the gap between structural performance and energy functionality. The work pioneers the integration of TiO? nanocomposites into cementitious matrices, offering a dual-purpose material for smart construction systems and embedded energy storage devices.
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    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, Fatih
    In 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.
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    Effect of inorganic salt solutions on consistency limits of kaolinite
    (2018) Varank, Gamze; Demir, Ahmet; Güvenç, Senem Yazıcı; Özçoban, Mehmet Şükrü
    This 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.
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    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 Badreddin
    Poly(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.
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    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, İbrahim
    A 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.
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    Grafen Nanotüp Takviyeli LED Kürlemeli Polyester Kompozitlerin Reolojik Özelliklerinin Araştırılması,
    (2022) Subaşı, Azime; Emiroğlu, Mehmet; Demir, Ahmet
    Son yıllarda nano teknolojinin gelişimine bağlı olarak nano partikül katkılı polimerik kompozitlerin üretiminde büyük bir artış olmuştur. Karbon nanaotüpler (CNT) iyi sertlik, yüksek dayanım, elektriksel özelliklerinin yanında mükemmel optik ve termal özellikleri sayesinde araştırmacıların dikkatini çekmiştir. Grafen nanotüp (GNT) olarak adlandırılan tek duvarlı karbon nanotüpler (SWCNT) polimer matrisli kompozit malzemelerde mekanik ve elektriksel özellikleri iyileştirmek amacıyla takviye malzemesi olarak kullanılmaktadır. Polimer matris içerisine eklenen nanomalzemeler sertleşmemiş kompozit reçinesi reolojik özelliklerinde önemli değişimlere neden olmaktadır. Kompozit malzeme üretiminde birçok farklı üretim yöntemi kullanılmaktadır. Farklı üretim yöntemlerinin gereksinim duyduğu reolojik özelliklerde farklı olmaktadır.Diğer taraftan polimer kompozitlerin üretiminde zararlı kimyasalların kullanımının azaltılması, enerji tasarrufu, üretim proseslerinin hız ve verimliliğinin arttırılması amacıyla UV/LED ile kürlenebilen fotobaşlatıcılar içeren polimerlerin kullanımı giderek yaygınlaşmaktadır.Bu çalışma kapsamında LED ile kürlenen polyester reçinelerinde GNT takviyesinin kompozit reçine karışımlarının reolojik özelliklerine olan etkileri deneysel olarak incelenmiştir. Farklı oranlarda (%0, 0.001, 0.003, 0.005, 0.010, 0.015, 0.020) GNTtakviye edilmiş LED ile kürlenen reçine karışımlarının zamana bağlı viskozite, kayma gerilimi ve kayma hızı değerlerindeki değişim incelenmiştir.Sonuç olarak GNT takviye edilen LED ile kürlenen polyester reçine karışımlarının viskozite ve reolojik özelliklerinde önemli değişimlere neden olduğu ve GNT takviyeli LED kürlemeli polyester reçinesinin viskozitesinin zamana ve kayma hızına bağlı olarak azaldığından dolayı tiksotropik davranış gösteren psödoplastik akışkan olduğu görülmüştür.
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    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, Şemsettin
    In 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.
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    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, Mustafa
    This 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.