Master Degree / Yüksek Lisans Tezleri
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Master Thesis Development of Conductive Oxide Based Thin Film Modified Electrodes and Biosensors Applications(Izmir Institute of Technology, 2021) Özyüzer, Lütfi; Yurttaş, Betül; Özyüzer, Lütfi; Erdem Gürsan, Kadriye Arzum; 01. Izmir Institute of Technology; 04.05. Department of Pyhsics; 04. Faculty of ScienceFrom 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 Manufacturing and Characterization of Perovskite Thin Films Using Novel Methods(Izmir Institute of Technology, 2020) Tekin, Hüseyin Cumhur; Sarı, Emre; Sarı, Emre; Tekin, Hüseyin Cumhur; 03.01. Department of Bioengineering; 04.04. Department of Photonics; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyPerovskite photovoltaics is a promising technology due to its low-cost fabrication and high efficiency. Since their first demonstration in 2009, efficiencies of perovskite solar cells (PSCs) increased unprecedently fast from 3.81% to 25.2% in 10 years. The most common method for the deposition of the absorber layer of the perovskite solar cells is the spin-coating method, which is not a scalable method, and this method is an obstacle to their commercialization. Efficiencies obtained with scalable methods are currently lower than that of the spin-coating method. In this thesis, among the scalable deposition methods, a novel ultrasonic spray-coating was used by adding antisolvent vapor to the system. The antisolvent quenching technique, that is commonly used to improve the crystalline quality of the film by spin-coating was successfully adapted for ultrasonic spray coating. The interaction between diethyl ether (DE) vapor, which is used as an antisolvent, and MAPb(I(3-x)Brx)3 precursor solution (where the solvent is DMF:DMSO, 4:1) was utilized to improve the crystalline quality of the perovskite film. As a result of this interaction, the intermediate phase was observed. The transition to the intermediate phase is supported by data from characterization methods such as optical microscopy, scanning electron microscopy (SEM), X-Ray diffraction (XRD), and current-voltage measurement. Furthermore, n-i-p devices with the FTO/c-TiO2/m-TiO2/MAPb(I(1-x)Brx)3/Spiro-OMeTAD architecture were produced with different antisolvent vapors and their efficiencies was compared. It was observed that devices using DE vapor reach higher efficiencies than devices without any antisolvent vapor.Master Thesis Anti-Reflective and Optical Transparent Coatings for Thin Film Solar Cells and Glasses(Izmir Institute of Technology, 2020) Özyüzer, Lütfi; Özyüzer, Lütfi; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyAntireflective 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; Öztürk, Orhan; Özyüzer, Lütfi; Özyüzer, Lütfi; Öztürk, Orhan; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyRecently, 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 Optical Characterization of Nanoscale Dielectric Films on Curved Surfaces Using Near Field Diffraction Method(Izmir Institute of Technology, 2019) Ataç, Enes; Dinleyici, Mehmet Salih; Dinleyici, Mehmet Salih; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyDemand on the high-quality optical thin films has increased because of the importance in the optical sensor technologies. The thicknesses of such films are usually shorter than the wavelength of visible light. Therefore, the optical characterization of these films is not a routine procedure especially on curved surfaces such as optical fiber. Besides, the methods in the literature and commercially available systems are either expensive, destructive or non-real time. In this thesis, it is aimed to propose a simple, inexpensive and non-destructive optical characterization method of nano-scale dielectric films on curved surfaces. The methodology of that approach can be described as the near field wavefront tracing diffraction by using structured light. In this way, it has been shown that sub-wavelength film thicknesses can be estimated. The proposed diffraction method is organized in four main stages. These are the coating of optical fibers, generation of structured light, determination of wave propagation via the near field Huygens-Fresnel wave-front tracing and sensing and processing of signal from the sensor array. Layer by layer assembly technique is used in coating process to keep under control the thickness of transparent film. Selection of various source types is about to changing of point spread function of applied field and observe the effects on intensity pattern. Using near field diffraction technique, sub-wavelength thickness of thin films can be predicted by taking the higher order components of diffraction pattern by recording at very close proximity to object. In this way, determination of thickness beyond the diffraction limits can be realized. Furthermore, the resolution of sensor array in sensing part is important since pixel size of the sensor array determines your detection limits to catch all variations on diffraction pattern. The whole process has a mathematical model with numerical analysis methods. This dissertation is about the proposing a mathematical estimation model for the optical properties of nano-scale dielectric films coated on curved surfaces. The experimental results show that near field Huygens-Fresnel wave-front tracing method by using structured light is a powerful technique.Master Thesis Growth and Characterization of Znsno Thin Films on Polymers for Oleds(Izmir Institute of Technology, 2019) Ekmekçioğlu, Merve; Aygün, Gülnur; Aygün Özyüzer, Gülnur; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe use of flexible organic light-emitting diodes (OLEDs) in smartphones and televisions with inclined screen shows significant improvements in commercial applications. Recently, flexible OLEDs have been used in lightweight, portable, wearable and even deformable screens, sensors as well as solid-state lighting applications. Under favour of these applications, remarkable developments are observed in the production of flexible electronics. The advantages of OLEDs according to the existing liquid crystal display (LCD) technology are self-emission capability, wide viewing angle, fast response time, simple structure, and low driving voltage. Highly conductive and transparent anodes are required for efficiency and uniform light emission in OLEDs. Indium tin oxide (ITO) which is one of the most promising anodes among transparent conductive oxides (TCO), has superior electrical and optical properties such as ~85% high transmittance at the visible region and ~104 Ω−1 cm−1good conductivity. The reason is due to the bandgap range of about 3.70 eV. Zinc tin oxide (ZnSnO or ZTO) is another TCO commonly used for many applications in the literature. Alternative anodes eliminate the use of ITO due to the absence of indium element so that highly desirable. In this thesis, ZTO is used as anode instead of ITO thin film and the eligibility of ZTO as an anode in OLED production is explored. The advantages of the optimized ZTO thin film according to the ITO are that is abundant on earth, has better performance, has low surface resistance, has less surface roughness, is capable of being produced as an anode in OLEDs. In this thesis to be successful, at the first stage ZTO thin films have grown on soda lime glass by magnetron sputtering, then ZTO and ZTO/Ag/ZTO multilayer thin films respectively have been deposited on flexible Polyethylene terephthalate (PET) and Polyimide (PI) substrates by magnetron sputtering method. In this way, the best coated thin films have been investigated using spectrophotometry, energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), Xray diffraction (XRD) and Raman spectroscopy.Master Thesis Improvement of Transparent Conductive Hybrid Ito/Ag Electrodes by Electro-Annealing(Izmir Institute of Technology, 2019) Uyanık, Zemzem; Uyanık, Zemzem; Aygün, Gülnur; Aygün Özyüzer, Gülnur; 04.05. Department of Pyhsics; 01. Izmir Institute of Technology; 04. Faculty of ScienceHibrit ITO/Ag/ITO (IAI) ince film tabaka yapılarının optik ve elektriksel performansları, ITO ve Ag katmanı kalınlığının fonksiyonu olarak incelenmiştir. Hibrit IAI ince filmleri borosilikat cam üzerine oda sıcaklığında yüksek vakum altında dc mıknatıssal saçtırma yöntemi ile üretilmiştir. Hibrit yapıdaki ITO, Ag, ITO filmlerin kalınlığı düşük tabaka direncine ve yüksek optik geçirgenliğe sahip olacak şekilde ayarlanmıştır. ITO katmanları arasındaki gömülü metal Ag katmanı, 10 nm ile 25 nm arasında değişen kalınlıklarda kullanılmıştır. IAI tabakası analiz edildikten sonra IAI ince filmlerin kristalliğini iyileştirmek için elektro-tavlama uygulanmıştır ve elektrik akımının IAI ince filmler üzerindeki etkisinin araştırılmasıyla elektronik cihaz ömrünün arttırılması amaçlanmıştır. Elektro-tavlamanın endüstriyel uygulamalar için daha uygun bir teknik olduğu sonucuna varılmıştır. IAI ince filmin yüzey direnci elektro-tavlama işleminden sonra 8.7 Ω/□ olarak bulunmuştur en yüksek geçirgenliğe ise 88.9% da ulaşılmıştır. Hibrit IAI ince filmlerin optoelektronik özellikleri, ITO film kristalliğini etkileyen ara katman olan metal Ag kalınlığına bağlıdır. Hibrit IAI ince filmlerinin yapısal özellikleri, CuK����� radyasyonuna sahip (�����=0.154 nm) X-ışını kırınımı (XRD) (Philips X'Pert Pro) ile tavlama sıcaklığının fonksiyonu olarak karakterize edilmiştir. IAI ince filmlerinin morfolojisi hakkında bilgi taramalı elektron mikroskobu (SEM) ile elde edilmiştir. IAI ince filmin optik geçirgenliği 200-2600 nm dalga boyu aralığına sahip PerkinElmerLambda 950 UV/Vis/NIR Spektrofotometre ile ölçülmüştür. Yüzey direnci ölçümleri için Keithley 2424 kaynak metrisi kullanılarak dört nokta yöntemi uygulanmıştır.Master Thesis Efficiency Studies of Cu2znsns2 Thin Film Solar Cell(Izmir Institute of Technology, 2018) Meriç, Ece; Aral, Gürcan; Özyüzer, Lütfi; Özyüzer, Lütfi; Aral, Gürcan; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyCu2ZnSnS4 (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 Development of Nanofiltration Membranes Through Surface Modification of Polysulfone Based Ultrafiltration Membranes(Izmir Institute of Technology, 2017) Bar, Canbike; Alsoy Altınkaya, Sacide; Alsoy Altınkaya, Sacide; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyStimuli responsive membranes have been used for suppressing fouling and regulating selectivity in different applications. These types of membranes are usually manufactured in thin film composite structure by either polymerizing stimuli-responsive monomer or coating stimuli-responsive polymer on a support. Responsiveness is due to their characteristic features which rely on reversible changes in mass transfer and interfacial properties as a result of changes in external environment such as pH, temperature and ionic strength. In this study, a pentablock copolymer (PBC) which consists of temperature responsive Pluronic F127 (PEO-b-PPO-b-PEO) in the middle block and pH responsive poly(N,N-(diethylamino)ethyl methacrylate) (PDEAEM) in the end blocks was used for designing a new type of thin film composite (TFC) nanofiltration membrane. The support of the composite membrane was prepared from a blend of polysulfone/sulfonated polyethersulfone using nonsolvent induced phase separation and the PBC was attached to the support via electrostatic interaction. The conformation of grafted PBC chains was determined by adsorption studies. The effects of PDEAEM block length, concentration of the copolymer and adsorption time on the adsorbed amount were investigated. Among three copolymer samples investigated (15, 20 and 25 kDa), the 25 kDa PBC displayed the highest responsiveness, thus, rejection properties were determined for the membranes prepared only from this sample. The influences of operation pH and temperature on the structure integrity of the membrane were investigated with pure water permeability measurements and the change in pore size was assessed by determining rejection of neutral solutes by the membranes. The membranes were further characterized with SEM, AFM, contact angle, XPS and zeta potential measurements. It was demonstrated that a new pH and temperature responsive, high flux TFC NF membrane was manufactured.Master Thesis Investigation of Sulfurization Temperature Effects on Cu2znsns4 Thin Flims Prepared by Magnetron Sputtering Method on Flexible Titanium Foil Substrates for Thin Flim Solar Cells(Izmir Institute of Technology, 2017) Buldu, Dilara Gökçen; Aygün, Gülnur; Aygün Özyüzer, Gülnur; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThis thesis presents the effect of sulfurization temperature on Cu2ZnSnS4 (CZTS) thin films on flexible titanium (Ti) foil substrates. The CZTS films was produced by using a two-stage method. In the first step, the metallic precursor layers Cu/Sn/Zn/Substrate were deposited on Ti foil substrate by using DC magnetron sputtering method. In the second step, the deposited metal precursors were sulfurized in a graphite box under Argon (Ar) ambient inside a tubular furnace under a definite temperature. To understand the effects of temperature on the formation of the CZTS structure several analyses were performed. Our samples, each with a different sulfurization temperature; ranging from 530 to 580 oC, were carried out and the structural properties of the absorber layer was determined. XRD measurements showed a sharp and intense peak coming from the (112) planes which was a strong evidence for good crystallinity. The intensity of (112) plane became a sharp and intense with increasing sulfurization temperature. Raman spectroscopy of the sulfurized thin films revealed that, the kesterite structure CZTS thin film were obtained with increasing sulfurization temperature. Electron Dispersive Spectroscopy (EDS) was also used for the compositional analysis of the thin films. EDS analysis showed that the films were grown with a Cu-poor Zn-rich composition. From these analyses we conclude that no interface formation occurred between the substrate and the CZTS thin films, hence, a buffer layer was not required. It was also seen that Ti foil was suitable as substrate for the growth of CZTS thin films with desired properties. We also conclude that the sulfurization temperature plays a crucial role for producing good quality CZTS thin films on Ti foil substrate.