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Öğe The C-V characteristics of TiO2/p-Si/Ag, GNR doped TiO2/p-Si/Ag and MWCNT doped TiO2/p-Si/Ag heterojunction devices(Elsevier, 2020) Erdal, Mehmet Okan; Kocyigit, Adem; Yildirim, MuratThe TiO2/p-Si/Ag, graphene (GNR) doped TiO2/p-Si/Ag and multi-walled carbon nanotube (MWCNT) doped TiO2/p-Si/Ag heterojunction devices were fabricated by electrospinning technique at same conditions. Their structural, morphological properties, thermal analyses (TGA), and capacitance voltage characteristics were studied and compared. The undoped, GNR and MWCNT doped TiO2 structures obtained successfully according to XRD measurements. Morphological properties of the undoped, GNR and MWCNT doped TiO2 composite structures have rod or ribbon like structures. The TGA result confirmed the GNR and MWCNT doped TiO2 structures. The C-V and G-V measurements were employed for electrical characterization of the TiO2/p-Si/Ag, GNR doped TiO2/p-Si/Ag and MWCNT doped TiO2/p-Si/Ag devices for various frequencies at room temperatures. The results imparted that the capacitance and conductance behaviors of all devices are strong functions of the frequency and voltage. The electrical parameters were calculated from C-2-V plots of the heterojunction devices and compared for three devices. The transient photocapacitance plots revealed that the devices can be employed for optical communication applications.Öğe A comparison of the electrical characteristics of TiO2/p-Si/Ag, GNR-TiO2/p-Si/Ag and MWCNT-TiO2/p-Si/Ag photodiodes(Springer, 2019) Erdal, Mehmet Okan; Yildirim, Murat; Kocyigit, AdemThe TiO2/p-Si/Ag, graphene nanoparticles doped (GNR) TiO2/p-Si/Ag and multi-walled carbon nanotube (MWCNT) doped TiO2/p-Si/Ag photodiodes were fabricated by electro-spinning technique at the same experimental conditions, and their structural, morphological and electrical properties were compared for photodiode applications. XRD measurements were confirmed undoped, GNR and MWCNT doped TiO2 structures, and brookite phase of (121) preferred orientation TiO2 has been observed from XRD patterns. SEM images of the heterojunctions showed that undoped and doped TiO2 layer have homogenous surfaces. I-V measurements were performed for electrical characterization of the TiO2/p-Si/Ag, GNR-TiO2/p-Si/Ag and MWCNT-TiO2/p-Si/Ag photodiodes under dark and light illumination conditions at room temperatures. The results imparted that all heterojunctions have good rectifying and photodiode properties. Some heterojunction parameters such as ideality factor, barrier height, series resistance were calculated and discussed in details according to thermionic emission theory, Cheung and Norde techniques. The determined ideality factor values are 8.55, 9.70 and 8.99, and barrier height values are 0.75 eV, 0.74 eV and 0.73 eV for the TiO2/p-Si/Ag, GNR-TiO2/p-Si/Ag and MWCNT-TiO2/p-Si/Ag photodiodes, respectively. These heterojunctions can be considered and improved as photodiodes in industrial applications.Öğe Dielectric characterization of Al/PCBM:ZnO/p-Si structures for wide-range frequency(Indian Acad Sciences, 2021) Yildiz, Dilber Esra; Kocyigit, Adem; Erdal, Mehmet Okan; Yildirim, MuratThe dielectric properties of the Al/PCBM:ZnO/p-Si structure were investigated using the impedance spectroscopy technique. PCBM:ZnO layer was obtained by spin coating method on the p-Si. The morphological properties of the PCBM:ZnO were investigated using atomic force microscopy. The results highlighted that PCBM:ZnO thin film has uniform surfaces. The dielectric parameters such as real and imaginary parts of the electric modulus (M ' and M '') and ac electrical conductivity (sigma), dielectric constant (epsilon '), dielectric loss (epsilon ''), loss tangent (tan delta) values were determined. The results of the dielectric properties of the Al/PCBM:ZnO/p-Si structures impressed voltage and frequency changing. The Al/PCBM:ZnO/p-Si structures can be regarded as a candidate for organic diode applications.Öğe Effect of Indium Doping on Optical Parameter Properties of Sol-Gel-Derived ZnO Thin Films(Walter De Gruyter Gmbh, 2019) Kocyigit, Adem; Erdal, Mehmet Okan; Yildirim, MuratZinc oxide (ZnO) has gained great interest for two decades, and its structural, optical, and electrical properties have been investigated by scientists for technological applications. The optical properties of ZnO provide an opportunity for its application in solar cells, lasers, and light-emitting diodes. We prepared ZnO thin films with various In doping levels by using a spin coating technique, and characterised their morphological and detailed optical properties for optical applications. According to the morphological properties obtained by atomic force microscopy, the film surfaces are homogeneous and the In doping level affects the surface morphology of the films. The optical properties of the films were investigated using an ultraviolet-visible spectrometer, and some optical parameters such as band gap, refractive index, extinction coefficient, single oscillator parameters, real and imaginary functions of the dielectric coefficient, and optical conductivity were calculated and discussed in detail. The various In doping levels affected the optical properties, and the In-doped ZnO thin films can find applications in industry.Öğe Effect of Indium Doping on Optical Parameter Properties of Sol-Gel-Derived ZnO Thin Films(Walter De Gruyter Gmbh, 2019) Kocyigit, Adem; Erdal, Mehmet Okan; Yildirim, MuratZinc oxide (ZnO) has gained great interest for two decades, and its structural, optical, and electrical properties have been investigated by scientists for technological applications. The optical properties of ZnO provide an opportunity for its application in solar cells, lasers, and light-emitting diodes. We prepared ZnO thin films with various In doping levels by using a spin coating technique, and characterised their morphological and detailed optical properties for optical applications. According to the morphological properties obtained by atomic force microscopy, the film surfaces are homogeneous and the In doping level affects the surface morphology of the films. The optical properties of the films were investigated using an ultraviolet-visible spectrometer, and some optical parameters such as band gap, refractive index, extinction coefficient, single oscillator parameters, real and imaginary functions of the dielectric coefficient, and optical conductivity were calculated and discussed in detail. The various In doping levels affected the optical properties, and the In-doped ZnO thin films can find applications in industry.Öğe Electrolyte performance of green synthesized carbon quantum dots from fermented tea for high-speed capacitors(Elsevier Science Sa, 2023) Baslak, Canan; Demirel, Serkan; Kocyigit, Adem; Erdal, Mehmet Okan; Yildirim, MuratIn recent years, obtaining carbon nanomaterials from natural products by natural methods has been among the most popular topics. The materials synthesized by this way have beneficial properties such as biocompatible, photostable and less harmful for environment. In this study, carbon quantum dots (CQDs) were synthesized by using fermented tea as a natural material and carbon source. The capacitor performance as an electrolyte was investigated with high-speed charge-discharge method as unusual in the literature. The characterizations of the CQDs were realized by HRTEM, XRD, XPS, UV-Vis absorption, and fluorescence spectroscopy techniques. The resulting particles have a size of about 10 nm according to HRTEM image. While the structural properties of the CQDs were confirmed by XRD and XPS, and optical behaviors were confirmed by UV-Vis and fluorescence spectroscopies. The electrochemical behavior of the obtained CQDs was tested as electrolyte material for capacitor applications. Experiments were carried out in three different operating potential windows in the 0-2 V range, and CQDs electrolytes exhibited high capacitive effect in symmetrical capacitors. However, the cyclic voltammetry (CV) analyses revealed that the CQDs electrolytes displayed a full supercapacitor electrolyte feature in the 0-0.5 V range. The CQDs electrolytes have a promising material for technological and industrial applications with their unique redox performance and high capacitive effect.Öğe Green synthesis capacitor of carbon quantum dots from Stachys euadenia(Wiley, 2024) Baslak, Canan; Demirel, Serkan; Dogu, Suleyman; Ozturk, Gulsah; Kocyigit, Adem; Yildirim, MuratCarbon quantum dots (CQDs) are a new type of carbon nanomaterial that has recently attracted great attention as a potential competitor to standard semiconductor quantum dots. There are various ways to synthesis CQDs, and one of harmless way is undoubtedly green synthesis. In this study, hydrothermal synthesis based on the green way was employed to synthesize CQDs. The CQDs were obtained using the green leaves of the Stachys euadenia plant extract, an endemic species located in Turkey. The CQDs were characterized by fluorescent and UV-Visible spectroscopy, and results confirmed blue emission (430-480 nm) and absorption around 280 nm. X-ray photoelectron spectroscopy (XPS) analysis revealed C=C, C-N and C-O interactions. X-ray diffractometer (XRD) patterns confirmed structure of carbon with a broad peak of (002) plane. High resolution tunneling electron microscopy (HRTEM) and dynamic light scattering (DLS) analysis was used to determine the shape and size of CQDs. The CQDs obtained from Stachys euadenia were employed as electrode materials for capacitor application, and they were tested in Swagelok-type cell by cyclic voltammetry (CV) measurements. CQD capacitors exhibited 2.12 F/g charge and 1.24 F/g discharge capacitances were obtained with similar to 58% coulombic efficiency rate for the first cycle. Results highlights that CQDs are synthesized successfully by green synthesis method and can be used for capacitor applications.Öğe Green synthesis of carbon quantum dots from Sideritis vuralii and its application in supercapacitors(Elsevier, 2023) Baslak, Canan; Ozturk, Gulsah; Demirel, Serkan; Kocyigit, Adem; Dogu, Suleyman; Yildirim, MuratQuantum dots have good optical and electrical behaviors and can be employed in solar cells, displays and supercapacitors. When new studies in nanoparticle as well as synthesis of quantum dots are examined, it can be seen that the interest in the green synthesis approach has increased. The green synthesis approach is so prom-inent due to an environmentally friendly method and does not contain toxic chemicals at the experimental stage. In this study, we used Sideritis vuralii (S. vuralii), which is endemic in Turkey, as a source of the green synthesis approach. We synthesized carbon quantum dot (CQDs) particles with the hydrothermal method from S. vuralii plant. We performed UV-Vis spectra, fluorescence spectra, XPS and DLS analyzes for the characterization of the CQDs. According to the size and characteristics results, the CQDs were successfully synthesized from the S. vuralii plant. Furthermore, we employed CQDs as electrode for capacitor applications, and cyclic voltammetry (CV) measurements were performed. The CV measurements indicated that CQDs electrodes have rechargeable sym-metrical capacitor behaviors with 10.42 F/g charge, 8.26 F/g discharge capacitances. The green synthesized CQDs can be improved for supercapacitor applications.Öğe The modification of the characteristics of ZnO nanofibers by TCNQ doping content(Springer, 2021) Erdal, Mehmet Okan; Koyuncu, Mustafa; Dogan, Kemal; Ozturk, Teoman; Kocyigit, Adem; Yildirim, MuratIn this study, the electrical properties of an Al/p-Si metal/semiconductor photodiodes with Tetracyanoquinodimethane-Polyvinyl chloride (TCNQ-PVC) and PVC-TCNQ:ZnO interfacial layers were investigated. Growing of the interfacial layers on p-Si were fulfilled using electrospinning method as a fiber form. Al metallic and ohmic contacts were deposited via physical vapor deposition method. Scanning electron microscopy (SEM) pictures of the devices were captured to examine the morphology of the structure. Within the scope of electrical characterization, I-V measurements of the Al/PVC-TCNQ/p-Si and Al/PVC-TCNQ:ZnO/p-Si devices were accomplished both in the dark and under illumination conditions. Various device parameters, such as ideality factor and barrier height values were determined from I-V characteristics. Although the ideality factor values were obtained as 8.47 and 6.85 for undoped and ZnO-doped Al/PVC-TCNQ/p-Si diodes, the barrier height values were calculated as 0.84 for both devices. When a comparison was made between ZnO doped and undoped Al/PVC-TCNQ/p-Si diodes, it was evaluated that the rectification and photoresponse properties of the heterojunction diode was improved with ZnO dopant.Öğe Photodiode behaviors of the AgSbS2 nanocrystals in a Schottky structure(Iop Publishing Ltd, 2021) Kocyigit, Adem; Erdal, Mehmet Okan; Ozel, Faruk; Yildirim, MuratCubic phase AgSbS2 nanocrystals (NCs) were synthesized by the hot-injection method, and they were inserted between the Al and p-Si to fabricate Al/AgSbS2/p-Si photodiode by the thermal evaporation method. AgSbS2 NCs were characterized by XRD, SEM and TEM instruments to confirm the crystal phase, surface morphology as well as crystalline size. The XRD pattern revealed that the cubic crystalline structure of the AgSbS2. The spherical shapes and well surface morphology were affirmed by SEM and TEM analysis. Al/AgSbS2/p-Si photodiode was characterized by I-V measurements depending on the light power intensity and by C-V measurement for various frequencies. I-V characteristics revealed that the Al/AgSbS2/p-Si exhibited good photodiode behavior and a high rectifying ratio. Various diode and detector parameters were extracted from I-V measurements, and they were discussed in detail. The C-V characteristics highlighted that the Al/AgSbS2/p-Si photodiode showed voltage and frequency dependent profile at the accumulation region. The fabricated Al/AgSbS2/p-Si photodiode can be thought for optoelectronic applications.Öğe Temperature dependent current-voltage characteristics of Al/TiO2/n-Si and Al/Cu:TiO2/n-Si devices(Elsevier Sci Ltd, 2019) Erdal, Mehmet Okan; Kocyigit, Adem; Yildirim, MuratWe fabricated undoped and Cu doped TiO2 thin films by spin coating technique and employed the films as interfacial oxide layer between the Al and n-type Si to investigate the effect of temperature on the Al/TiO2/n-Si and Al/Cu:TiO2/n-Si devices. For that aim, the I-V measurements were performed in the range of 50 K-400 K by 50 K interval. The devices exhibited good rectifying behavior and thermal response in a wide range temperature. Ideality factor, barrier height and series resistance were calculated from I-V measurements for various temperatures by thermionic emission theory, Norde and Cheung methods and discussed in the details. The obtained results revealed that the device parameters are a strong function of the temperature. The interface states (N-ss) were affected by the changing of the temperatures. The Al/TiO2/n-Si and Al/Cu:TiO2/n-Si devices can be performed for wide range temperatures in various technological applications.
