Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis The Effect of Bending Cycles on Optical and Electrical Properties of Multilayer Zto Ag Zto and Ito Transparent Conductive Oxide Thin Films Grown by Magnetron Sputtering(01. Izmir Institute of Technology, 2024) Çelikli, Cenkay; Özyüzer, Lütfi; Özdemir, MehtapBu tez, esnek yüzeylerde büyütülen Çinko Kalay Oksit (ZTO, Zn2SnO4)/Ag/ZTO (ZAZ) ve İndiyum Kalay Oksit (ITO, In2O3:SnO2) ince filmlerin yapısal, elektriksel ve optik özelliklerini incelemektedir. Karşılaştırma, İndiyum elementinin azalan bulunabilirliği ve yüksek maliyetleri nedeniyle yapılmıştır. Bu doğrultuda, gümüş ile tamamlanan ZTO tabanlı bir sandviç yapı geliştirilmiştir; bu yapı, yüksek iletkenlik ve şeffaflık gerektiren Şeffaf İletken Oksit (TCO) uygulamalarında ITO'ya benzer özellikler sunmaktadır. Deneysel çalışmalarda, magnetron sputtering tekniği kullanılarak ince film kaplama için optimum parametreler belirlenmiş ve polikarbonat yüzeyler üzerine örnekler büyütülmüştür. Yapısal karakterizasyon için yapışma testleri, profilometri ve Taramalı Elektron Mikroskobu (SEM) kullanılmış; elektriksel özellikler 2-probe ve 4-probe yöntemleriyle, optik özellikler ise spektrofotometre ile ölçülmüştür. Sonuçlar, ZAZ çok katmanlı yapısının ITO kaplamalarına kıyasla daha iyi performans sergilediğini göstermiştir. Bu çalışma, ZAZ ince filmlerinin ITO yerine kullanılabileceğini ve esnek giyilebilir teknolojilerdeki gelecekteki uygulamaları için bir rehber sunduğunu ortaya koymaktadır.Master Thesis Development of Conductive Oxide Based Thin Film Modified Electrodes and Biosensors Applications(Izmir Institute of Technology, 2021) Yurttaş, Betül; Özyüzer, Lütfi; Erdem Gürsan, Kadriye ArzumFrom the first biosensor produced in 1956 to the present day, biosensors have been highly developed and diversified. In biosensor manufacturing, thin films have become a rapidly emerging field. Depending on the thin film material used, thin films have many advantageous properties for biosensors, such as high surface-to-volume ratio, conductivity, stability, specificity, biocompatibility, and good electrocatalytic activity. Dopamine is a neurotransmitter that has a significant impact on the emergence and treatment of certain diseases such as Alzheimer's and Parkinson's diseases. Dopamine monitoring is important for the prevention of these diseases, and it is a favorable option to use biosensors, which are useful and practical tools, instead of time-consuming and expensive conventional methods. For this purpose, in this thesis, a non-enzymatic electrochemical biosensor based on thin film electrodes was developed for monitoring dopamine levels. The electrodes were developed by deposition of Zn2SnO4 (ZTO) thin film on ITO thin film substrate by DC magnetron sputtering technique. The properties of the electrodes were determined by thickness, optical transmittance, XRD and SEM analysis. Electrochemical analysis, namely CV, EIS and DPV measurements, were performed before and after the electrodes were sonicated and modified with APTES before their application to the voltammetric detection of dopamine. In addition, electrochemical measurements were performed before/after sonication, APTES modification. Dopamine was detected by a voltammetric method using DPV technique. Furthermore, experiments in the presence of interferents such as ascorbic acid (AA), uric acid (UA) etc. showed that the thin film electrodes can be successfully applied for voltammetric determination of dopamine. As a result, the biosensor technology developed in this study has the potential to be wearable in the future, enabling non-invasive monitoring of dopamine levels in body fluids such as saliva, tears and sweat.Master Thesis The Growth of Vanadium Dioxide Thin Films by Magnetron Sputtering Technique and Terahertz Wave Modulation Characteristics(01. Izmir Institute of Technology, 2020) Ata, Bengü; Özyüzer, LütfiVanadium dioxide (VO2) is a fascinating material thanks to its unique insulator-metal transition (IMT) at 68 °C which is very close to the room temperature. This reversible change in electrical resistivity is around several orders of magnitude and the electrical change accompanied by optical and structural change as well. Thanks to these unique properties vanadium dioxide material has been studied intensively past decades. This phase transition allows us to apply the transition properties widen application such as field effect transistor (FET), uncooled bolometers, tunable metamaterial filters, high data rate wireless communication etc. Especially for terahertz region which is the most unexplored region of the electromagnetic spectrum, vanadium dioxide is a promising material having ability to modulate terahertz waves by IMT phenomena. In this work, vanadium dioxide (VO2) thin films fabricated by reactive DC magnetron sputtering method and its properties optimized to minimize the amounts of secondary phases by optimizing the oxygen concentration, sputtering power and deposition time. Samples which show the maximum resistivity change during the transition have been used for the terahertz modulation experiments. It has been observed that when the VO2 samples triggered by continuous wave (CW) laser, VO2 transforms to the metallic phase, behave as an opaque material to the terahertz wave. At room temperature, in insulating phase it is partially transparent to terahertz radiation. This results indicate that VO2 thin films can be a good candidate for THz wave modulators.Master Thesis Anti-Reflective and Optical Transparent Coatings for Thin Film Solar Cells and Glasses(Izmir Institute of Technology, 2020) Kamolov, Shukrullo; Özyüzer, Lütfi; Özyüzer, LütfiAntireflective coatings in some implementation necessary for the decreasing surface reflection, but in some applications also for increasing transmittance. Incident radiation on the surface of the optical material is divided into transmitted, reflected, scattered, and absorbed proportions, and the proportion of current energy that deployed among them is defined by RI (refraction indices). Solar panels made from crystalline or polycrystalline silicon, but another type of solar panel is a thin-film solar panel. Thin-film technology has several advantages, such as low material consumption, which leads to cost savings to production, the ability to absorb diffused solar radiation, a relatively high efficiency (up to 20%), long service life (efficiency decreases by 10-15% of the initial efficiency). For all types of photovoltaic devices, energy loss is an important issue. Single-layer and two-layer antireflection coatings with a low refractive index, coated and uncoated (SiO2) thin-film with the sol-gel method were prepared and compared in terms of performance and continuity. The photocatalytic performance of (SiO2) thin films in 1, 2, 3, 4, 5 and 24 hours was defined with methylene blue dye solution (20 mL) under UV source and was illuminated by it. The I-V characteristics curve of solar cells for small and large area was learned and increasing efficiency was observed. Adhesion tests in this study was applied by tape tests on substrates of glass. As a result, the field tests of small and large area glasses coated solar panels were realized, the low reflectance and high efficiency were obtained.Master Thesis The Effect of Metal Doping on Tio2 for Photocatalytic Applications(Izmir Institute of Technology, 2019) Alduran, Yeşim; Özyüzer, Lütfi; Öztürk, OrhanRecently, the photocatalysis method has been an active research area as a promising solution for environmental cleaning method, leading to self-cleaning and sterilization of solar cell surfaces to produce water dissociation reaction. Titanium dioxide (TiO2) is the most suitable semiconductor for photocatalytic applications due to its high oxidation potential and high efficiency when irradiated by ultraviolet light (UV). Undoped and Ruthenium (Ru+) doped TiO2 thin films were prepared using magnetron sputtering technique. All thin films were grown on SLG different ratios like 1 sec, 3 secs, 5 secs and 7 secs to set shutter position in magnetron sputter target. Transparent substrate SLG is coated with nearly 50 nm TiO2 thin films without compromising any optical properties. Samples were heat treated for two hours at 500°C to get the anatase phase crystal structure. The crystallization peaks of TiO2 are proved to get the anatase phase. Photocatalytic activity of TiO2 thin films are determined after 1, 3, 5 and 24 hours with organic pollution as a methylene blue dye degradation under UV light. The degradation of methylene blue was investigated kinetically and photocatalytic activity rate constants of the photocatalysts were calculated. All thin films could not reach super hydrophilicity state. Undoped TiO2 contact angle 47.309o and Ru doped TiO2 63.218o were evaluated. The photocatalytic degradation percentage of Methylene Blue was reached 87%, after 24 hours of UV irradiation, when using Ru-doped TiO2 thin film. Consequently, the anatase phase of Ru-doped TiO2 thin films are found best photocatalytic activity in self-cleaning performance.Master Thesis Efficiency Studies of Cu2znsns2 Thin Film Solar Cell(Izmir Institute of Technology, 2018) Meriç, Ece; Özyüzer, Lütfi; Aral, GürcanCu2ZnSnS4 (CZTS) is a promising candidate as an absorber layer for thin film solar cells due to not only its low cost but also nontoxic properties contrary to alternative materials such as CdTe and Cu(In,Ge)Se2 (CIGS). Recently, CZTS and similar chalcogenides have attracted remarkable attention because of their suitable properties. In my thesis; I studied the efficiency of Cu2ZnSnS4 thin film solar cells for various stoichiometric cases. Besides, the effect of back contact, buffer layer thickness and sulfurization time were investigated. CZTS thin films were fabricated by DC magnetron sputtering method on Molybdenum (Mo) coated Soda Lime Glass (SLG) and Ti foil substrates. Cu, Sn, Zn, Cu layers were, respectively, deposited on the substrates, and then sulfurization process was followed as the second step in the growth process to obtain a desirable CZTS formation. The as grown CZTS structure was investigated using Raman and X-Ray Diffraction (XRD) spectroscopies. Scanning electron microscopy (SEM) was used to investigate the surface morphology of the films. Energy dispersive spectroscopy (EDS) was used to define the chemical structure of the surface of the films. Next, a CdS buffer layer was deposited on CZTS absorber layer using CBD method at 85oC for varying times (60, 75 and 90 min). Then, ZnO and Al doped ZnO (AZO) layers were deposited on CdS. J-V curves were obtained for SLG/Mo/CZTS/CdS/ZnO/AZO solar cell structure. The photovoltaic characteristic of solar cells was studied and their dependence on CdS deposition time were found. Among all the device we produced, the highest efficiency was obtained for the device with the lowest CdS deposition time. In addition; effect of sulfurization time on the solar cell conversion efficiency was studied.Master Thesis Temperature Dependence of Resistivity and Hall Coefficient in Cu2znsns4 Absorbers for Thin Film Solar Cells(Izmir Institute of Technology, 2017) Akça, Fatime Gülşah; Aygün Özyüzer, Gülnur; Özyüzer, Lütfienergy is the most powerful clean energy source to act on the current energy needing all over the world. The utilization of green energy systems should be promoted since these energy systems benefit consumers, industry and the environment effectively for the developing countries. This advancement can be solely achieved if renewable energy sources become more accessible. It means that not only cheaper but also handy clean energy systems are needed. In spite of relatively high efficiency obtained by using c-Si, Si solar modules require high budget for manufacturing. The high production cost of c-Si, PV industry is lead to search for cheaper candidate materials like Cu2ZnSnS4 (CZTS) as absorber layer in solar cells. The aim of the thesis is to investigate electrical properties of CZTS p-type intrinsic semiconductor compound on soda lime glass substrates, including the temperature dependent electrical conductivity, carrier concentrations and mobility extracted from Hall Effect measurements. Firstly, the metal precursor films were fabricated in multi-target sputtering system, then they were sulfurized inside the tubular furnace in order to obtain the CZTS compound. X-ray diffraction and Raman spectroscopy measurements revealed the formation of kesterite structure. A good crystallinity and grain compactness of the films were determined by scanning electron microscopy (SEM). Electrical properties were measured by van der Pauw techniques. Hall effect measurements showed the p-type semiconductor behavior for all samples at room temperature. Also, optical properties including absorption coefficient, spectral transmission, and optical band gap were determined to characterize CZTS thin films.Master Thesis Ionic Conductivity of Li0.5la0.5ti1-Xalxo3 Electrolytelayer for Thin Film Batteries(Izmir Institute of Technology, 2016) Ulusoy, Seda; Özyüzer, Lütfi; Aral, GürcanIn this study, crystalline lithium lanthanum titanium (aluminum) oxide Li0.5La0.5Ti1-xAlxO3 (LLTO) powder targets with different Aluminum (x) content were prepared by conventional solid state reactions as Li0.5La0.5TiO3, Li0.5La0.5Ti0.99Al0.01O3, Li0.5La0.5Ti0.95Al0.05O3, Li0.5La0.5Ti0.90Al0.10O3 and Li0.5La0.5Ti0.85Al0.15O3 compositions. Then, after a couple of calcination processes with regrinding of the prepared stoichiometric powder batch, it is placed into Cu-base plate to be pressed in order to provide a compact, dense and smooth target surface for the thin film deposition. For the thin film fabrication, radio frequency (RF) magnetron sputtering technique is used to sputter the dielectric target. Thin films were deposited on soda-lime glass (SLG) and 256 nm thick indium tin oxide (ITO) layer grown on soda-lime glass (SLG) substrates. For the electrical measurements of LLTO thin film, it was fundamental to have ITO as conducting layer electrode. Targets with various Al (x) compositions were deposited for the investigation of Ti substitution with Al on structural and electrical properties. Besides, crystalline structure of the targets was characterized by X-ray powder diffraction (XRPD) and Raman Spectroscopy analysis while structural, morphological and compositional properties of the thin films were determined by x-ray diffraction (XRD), scanning electron microscope (SEM) and x-ray photoelectron spectroscopy (XPS) respectively. Moreover, in order to understand the effect of Al doping on ionic conductivity, electrical measurements were performed at room temperature by AC impedance spectroscopy forming ITO/LLTO/Al capacitor like structure. Maximum ionic conductivity result is obtained for Li0.5La0.5Ti0.95Al0.05O3 thin film composition. Also, temperature dependent ionic conductivity measurements were performed from 298 K to 373 K to evaluate activation energy for the Li-ion conduction. Keywords: Ionic conductivity, Li0.5La0.5Ti1-xAlxO3, electrolyte, thin film, activation energy, RF magnetron sputteringMaster Thesis Characterization of Vanadium Oxide Thin Films Grown by Magnetron Sputtering Technique(Izmir Institute of Technology, 2015) Yüce, Hürriyet; Özyüzer, LütfiVanadium dioxide (VO2) exhibits metal insulator transition (MIT) at around 70 °C. VO2 shows insulator phase at low temperature whereas above the transition temperature VO2 shows metallic phase. The resistivity of this material abruptly changes by a factor of 104 at MIT temperature. There are some factors which induce MIT in VO2 structure such as electric field, the change in temperature or doping. Due to these properties, VO2 is an interesting candidate for exploring potential applications in high speed electronic devices. VO2 plays an important role for field effect transistor (FET) applications. VO2 with its peculiar properties is a good candidate for channel material in FET. Electric field triggered MIT is a desired feature for FET applications. In this work, VO2 thin films have been deposited on c-cut sapphire [Al2O3(0001)] substrate by using DC magnetron sputtering technique. In order to obtain the homogeneous VO2 thin film, the growth process was carried out at various oxygen flow rates with different deposition time. To obtain single VO2 phase, optimum oxygen rate was investigated with various analysis techniques such as Raman, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and optical-electrical measurements. At the same time, the temperature dependences of optical-electrical properties of these films were analyzed. Then, the metal insulator transition was observed with the change in resistivity by a factor of 104 which is the highest value among grown VO2 films by sputtering technique in the literature. For FET applications, the grown VO2 thin film which indicates the highest change in resistivity at transition temperature was patterned by electron beam lithography in order to create FET channel schema. After electron beam lithography process, the electrical properties of the VO2 strips with various widths were analyzed. The effects of the widths of the VO2 strips on their electrical properties were investigated.Master Thesis Indium Tin Oxide (ito) Coating on Cylindricalsurfaces: Electrical and Structural Characterization(Izmir Institute of Technology, 2015) Arslan, Halil; Aral, Gürcan; Özyüzer, Lütfi; Özyüzer, Lütfi; Aral, GürcanOptical transparent conductive oxides (TCOs) which were discovered in the first quarter of twentieth century, and which belong to the class of semiconductor elements, are the constituent of today’s and future technology thanks to the high optical transparency ( ≥ % 85) they have in the visible region (390- 700 nm), and to the low electrical resistivity they have (10-4 ohm.cm). One of the most common usage of optical transparent conductive oxides; which have a quite extensive application area from transistors to solar panels, from flexible screens to OLEDs; is the textile materials known as smart clothes. The use of TCOs in textile materials, generally occurs by means of electrochromic structures that have the feature of changing color. In the most general sense, electrochromic structures can be defined as the materials that change their colors, which they gain thanks to reduction and oxidation reactions under a low potential difference of 1.5 – 5V, as a transition from one color state to another or from colorless state to color state. Even though they differ according to their area of utilization, electrochromic structures are generally consisted of seven layers as; Surface / conductive thin film (TCO) / Electrolyte film / Ionic conductive layer / Opposite electrolyte film / Conductive thin film (TCO) / and Surface. Electrical conductor and optical transparent indium doped tin oxide (ITO) film that are of vital importance in electrochromic fiber structures, were deposited on the fiber surface along with the specially-designed magnetic sputter in order to coat the cylindrical surfaces within the scope of the thesis. Film deposition was repeated by replacing the ionizing gas (Ar) flow rate and the energy applied. While the structural characterization of thin films was carried out by means of optical microscope and scanning electron microscope (SEM), electrical characterization of deposited thin film, was carried out by a multi-meter (Ohm meter). In addition, the thickness of thin film that was magnified on the surface of the fiber, was calculated by SEM particularly, and also by different methods. As a result of the analyzes carried out, it was observed that ~ 40 sccm ionizing gas flow rate, 90 W applied energy, and 119 cm/min fiber feed rate increased the quality of the thin film acquired.
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