Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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Now showing 1 - 8 of 8
  • Doctoral Thesis
    Dielectric Film Characterization Beyond Classical Limits Exploiting Spatially Structured Entangled Photon Pairs
    (01. Izmir Institute of Technology, 2024) Ataç, Enes; Dinleyici, Mehmet Salih
    Kuantum optiği, ışığın farklı kuantum durumlarını üretmeye, manipüle etmeye ve tespit etmeye odaklanan yeni fırsatlar, alternatif metodolojiler ve potansiyel olarak çığır açıcı teknolojiler sunar. Bu alan enstrümantasyon, ölçüm ve metrolojide keşif ve uygulama için yeni yollar açmaktadır. Buradan hareketle tezin temel amacı, klasik sınırların ötesinde bir optik fiber üzerindeki ultra-ince şeffaf dielektrik filmlerin kalınlık karakterizasyonuna dayalı yeni bir kuantum dolaşıklık tabanlı faz kırınım şeması önermektir. Ek olarak, önerilen sistemde çakışma tespiti ve optik tutarlılık önemli bir rol oynadığından, standart bir CCD kamera kullanarak mekansal olarak dağıtılmış yoğunluk verilerinden zaman aralığı bilgisini çıkararak termal ışık karakterizasyonu için pratik ve karmaşık olmayan bir ölçüm prosedürü de sunuyoruz. Yukarıda belirtilen amaçları gerçekleştirmek için öncelikle kuantum dolanıklığın ölçüm sistemleri üzerindeki etkisini, özellikle de doğası gereği daha iyi çözünürlük sunduğundan, optik mikroskopiyi inceledik. Daha sonra, uzaysal dolaşıklık kavramı, kavisli bir yüzey üzerinde dielektrik film karakterizasyonu için faz kırınım şeması ile entegre edilir. Termal fotonlarla alternatif bir konfigürasyon da gösterilmiştir. Sonuçlara göre, şeffaf dielektrik filmlerin kalınlığı, ilgilenilen dalga boyunun yirmide birinin altında doğrulukta tahmin edilebilmektedir. İkinci bölümde, termal ışık foton istatistiklerinin ve ikinci dereceden tutarlılık fonksiyonunun çıkarılması için geleneksel bir CCD kameranın tek piksel yoğunluk ölçümlerinden yararlanarak kavram kanıtı deney düzeneğini tanıttık. Böylece, kümelenmiş ışık olgusunun tutarlılık süresinin ötesinde kullanıma hazır dedektörlerle gözlemlenebileceğini kanıtladık. CCD kameranın kapsamlı bir fizibilite analizi de rapor edilmiştir. Son olarak, sonuçlar artıları ve eksileri ile değerlendirilerek gelecekteki çalışmalar için bir yol haritası çizilmiştir. N-katlı algılama şeması, pompa tutarlılığının karakterizasyon sistemi üzerindeki etkisi ve önerilen foton istatistik kurulumunun pratik mühendislik uygulamaları dahil olmak üzere umut verici perspektifleri kısaca açıkladık.
  • Doctoral Thesis
    A Comparative Study of Thin-Film Coated Silicon Wafer Surfaces for Laser-Induced Breakdown Spectroscopic Analysis of Liquids
    (01. Izmir Institute of Technology, 2021) Aras, Nadir; Yalçın, Şerife Hanım
    Laser-Induced Breakdown Spectroscopy, LIBS, is a relatively new atomic emission spectroscopic technique that shows rapid growth due to its many special peculiarities, like its ability to provide spectral signatures of all chemical species at the same time, in all environments of solid, liquid, or gas. Liquid sample analysis by LIBS is more troublesome compared to analysis of solids. Therefore, liquid analysis by LIBS requires some pretreatment steps to be applied before direct analysis of the samples. In the literature, a variety of approaches has been successfully applied and there is still plenty of room to improve methodologies used in the liquid-LIBS analysis. The main purpose of this thesis study was to perform studies for the development of a LIBS-TARGET for sampling liquids on it, after drying, by repetitive laser pulses. With this purpose, silicon wafer-based substrates with differing surface compositions; uncoated (crystalline silicon, c-Si), oxide-coated silicon, SiO2, and nitride coated silicon, Si3N4, were tested for several experimental parameters. Within the content of this study, a fast and accurate methodology for direct analysis of aqueous samples by LIBS is proposed. This methodology has two important attributes: one is the use of the non-metal substrate, silicon wafer, for the first time for direct analysis of aqueous samples dried on, and two is the use of high energy laser pulses focused outside the minimum focal point of a plano-convex lens at which relatively large laser beam spot covers the entire droplet area for plasma formation. Si-wafer-based substrates were used for both qualitative and quantitative analysis of Cd, Cr, Cu, Mn, and Pb elements, and analytical figures of merit were determined. The analytical performance of each substrate was evaluated from the experiments performed with aqueous standards and real water samples. Silicon nitride-coated substrate has shown superior properties in terms of enhancing the LIBS signal and as low as 11 pg detection limits for Pb were obtained.
  • Doctoral Thesis
    Terahertz Imaging Applications and Characterization of Ito Thin Films Grown by Magnetron Sputtering
    (Izmir Institute of Technology, 2020) Köseoğlu, Hasan; Özyüzer, Lütfi
    THz radiation (0.1-10 THz) has unique properties not found in other parts of the electromagnetic spectrum. THz technological applications need high-performance THz imaging and spectroscopy system components such as THz filters, modulators, reflectors. Transparent conducting oxides (TCOs) meet these needs in the THz field. Indium tin oxide (ITO) thin film is one of the most used materials among the TCOs. However, the research on the THz properties of ITO film is currently at an early stage. In this thesis, ITO thin films were deposited on borosilicate (BS), fused silica (FS) and PET substrates using large area magnetron sputtering system. Optical, structural and electrical properties of the ITO films on different substrates were analyzed. Moreover, the effect of electro-annealing in vacuum and air on the properties of ITO films grown on BS and FS substrates were investigated. Furthermore, CW THz imaging system were designed to take THz images of some objects and to analyze THz properties of ITO films grown on FS and PET substrates. Our findings indicate that electrical, structural and optical properties of ITO films can be improved by electro-annealing in air and vacuum. We addressed that electro-annealing in vacuum is more appropriate technique for the applications in industry. We also addressed the importance of oxygen partial pressure and ITO film thickness to adopt them as a transparent electrode in flexible devices. Moreover, our analysis about the THz properties of ITO films on FS and PET substrates showed that fabricated ITO films have potential application in THz field such as THz filters, modulators and reflectors.
  • Doctoral Thesis
    Optical and Electronic Properties of Atomically Thin Layered Materials: First Principles Calculations
    (Izmir Institute of Technology, 2019) İyikanat, Fadıl; Senger, Ramazan Tuğrul; Şahin, Hasan
    The extraordinary interest in two-dimensional (2D) materials is increasing day by day. Thanks to advances in the experimental techniques, monolayer form of another material is synthesized every day with features not seen in the bulk form. Ab initio methods provide useful tools for characterizing and functionalizing the various properties of these materials. The results obtained through first principles quantum-mechanical calculations can help to predict and understand the experimental data, such as the position and source of the spectroscopic peaks in the Raman or optical absorption spectra. The aim of this thesis is to predict and functionalize the optical and electronic properties of atomically thin layered materials using density functional theory and approaches beyond. Within the scope of this thesis, possible technological applications of various 2D materials ranging from perovskite crystals to transition metal dichalcogenites are investigated by using several functionalization methods. In order to accurately predict the optical properties of these materials, it is very important to use approaches that take into account the many-body effects. Recent studies have shown that many-body perturbation theory in the form of GW approximation is highly reliable to calculate the quasiparticle properties of materials. By solving the Bethe Salpeter equation on top of GW calculation, the quasiparticle energies and excitonic properties, which have dominant effect in the optical properties of ultra-thin materials are examined in detail.
  • Doctoral Thesis
    Experimental and Computational Investigation of Transport Phenomena in Initiated Chemical Vapor Deposition (icvd) Process
    (Izmir Institute of Technology, 2017) Ateş, Selcan; Ebil, Özgenç; Ebil, Özgenç
    As a polymer thin-film deposition technique, initiated CVD (iCVD) is a heterogeneous process involving gas phase precursors and solid film formation on a solid/liquid substrates at different temperature regions. Obtaining fine-tuned film properties over different substrate geometries at different process conditions is a challenging tasks and requires experimental trials. The major goal of this study is to develop a computational model which describes all relevant transport phenomena occurring in iCVD process, and which is capable to predict the polymer film thickness at different deposition conditions for flat and/or non-flat substrates in a 3D reactor geometry. A Finite Element Analysis (FEA)-based 3D computational model, which can be applied to a variety number of iCVD reactor and substrate geometries, has been developed in the study. To validate the model, reported experimental conditions of 1H,1H,2H,2Hperfluorodecyl acrylate (PFDA) deposition with t-butyl peroxide (TBPO) initiator, and butyl acrylate (BA) deposition with t-amyl peroxide (TAPO) initiator, are applied to the model, respectively. The simulation results of both deposition processes show good agreement with experimental results reported in literature. Presented model successfully describes the relevant transport phenomena, and provides a priori predictions on polymerization rate, and film thickness on complex substrate geometries for a polymerization reaction with known kinetic data. For further studies, presented model can be modified or used as an approach for modeling of other types of CVD systems as well as facilitating process scale-up. The model can also extract valuable polymerization kinetics data provided that a sufficient number of experiments are performed at a specified substrate temperature, and process parameters and measured final film thicknesses are entered to the model.
  • Doctoral Thesis
    X-Ray Photoelectron Spectroscopy Analysis of Magnetron Sputtered Cu2znsns4 Based Thin Film Solar Cells With Cds Buffer Layer
    (Izmir Institute of Technology, 2017) Cantaş Bağdaş, Ayten; Özyüzer, Lütfi
    Cu2ZnSnS4 (CZTS) is a novel quaternary compound which contains Cu, Zn, Sn and S elements. It is a p-type semiconductor which has been taken attention in the last years as an absorber layer. Since it consists of abundant, low cost and non-toxic elements, it is one of the most promising candidate as an absorber layer for thin film photovoltaic (PV) application. Having high absorption coefficient, low bandgap value which is theoretically in desired range make this material attractive for solar cell application. In this thesis, CZTS absorber layers were grown using two stages which are the magnetron sputtering of metallic precursors, followed by a heat treatment under sulfur vapor atmosphere. Two types of CZTS were grown such as SLG/Mo/Cu (55nm)/Sn/Zn/Cu (120nm) and SLG/Mo/Cu (120nm)/Sn/Zn/Cu (55nm). For the same stacking order, the effect of Cu thickness sequentially grown with Sn layer on the film quality were investigated. The optical properties, microstructure, surface and bulk composition of CZTS films were investigated in detail. This study revealed a correlation between the CZTS stacking order having different thickness of Cu layer and the improvement of film quality, which was also confirmed by the photo-conversion efficiency of the fabricated devices. In this work, the other investigated layer is CdS which is an n-type semiconductor with bandgap energy of 2.4 eV. Since CdS has well lattice match with the heterojunction between CdS and CZTS, it is one of the most preferred material as a buffer layer for solar cells. In this work CdS buffer layers were deposited by chemical bath deposition technique. The optimization of CdS layers were occurred and optical, structural, bulk and surface compositions were investigated in detail. Finally, SLG/Mo/CZTS/CdS/i-ZnO/AZO devices were fabricated. The effect of structure properties of CZTS films and the thickness of CdS buffer layer on efficiency of fabricated solar cells were investigated.
  • Doctoral Thesis
    Magnetron Sputtering Growth of Azo/Zno Multilayers for Cu2znsns4 Thin Film Solar Cells: Material and Device Characterization
    (Izmir Institute of Technology, 2017) Köseoğlu, Fulya; Özyüzer, Lütfi; Aygün Özyüzer, Gülnur
    Cu2ZnSnS4 (CZTS) absorber layer attracts so much attention in photovoltaic industry since it contains earth abundant, low cost and non-toxic elements contrary to other chalcogenide based solar cells such as CuInGa(S,Se)2 (CIGS) and CdTe. Although, CZTS studies have been newly started, recently 9.4 % efficiency has been achieved. In the present thesis, all layers used in the CZTS device structure were investigated using energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscopy (SEM), spectrophotometry and Raman spectroscopy. For CZTS absorber layer, CZTS films based on a stacked precursor (Cu/Sn/Zn/Cu) were prepared. The effect of sulfurization time and the thickness of top and bottom Cu layer in precursors on the properties of CZTS thin films were investigated. We addressed the importance of Cu layer thickness adjacent to Sn to avoid developing detrimental phases and to get complete formation of kesterite CZTS absorber layer. We also addressed the importance of sulfurization time to restrict the Sn and Zn losses, formation of oxides such as SnO2 and ZnO, formation of MoS2 and voids between Mo/CZTS interface. Effect of the sulfur concentration on the properties of Zn(O,S) thin films were investigated. We showed that key parameters such as energy gap and crystal structure of the Zn(O,S) thin films can be tuned by changing the sulfur concentrations of the films. We succeed substitute conventionally used CdS buffer layer with environmentally friendly alternative Zn(O,S) buffer layer in CZTS solar cells. Effect of substrate position and rotation speed during the deposition of AZO thin films were investigated. We addressed that stress on the films can be significantly reduced by off-center deposition and rotating the sample holder during the deposition. In this way, high transmission in the visible range and metal like resistivity were achieved simultaneously at room temperature. We observed strong dependence of device performances on both sulfurization time and the thickness of Cu layer adjacent to Sn in CZTS absorber. The best device was based on CZTS films sulfurized for 30 minutes and having thicker Cu layer adjacent to Sn layer in precursors.
  • Doctoral Thesis
    Preparation of Hydroxyapatite/Silk Protein Thin Film Implant Surfaces, Investigation of Their Microstructural Properties and Model Protein Interactions
    (Izmir Institute of Technology, 2009) Özcan, Selçuk; Çiftçioğlu, Muhsin
    Biocompatible hydroxyapatite (HAp) coatings of load bearing metallic in vivo hard tissue implants act as local scaffolds for enhanced osteoconduction, providing fast bone apposition and cementless fixation. In this study, in an attempt to exploit the potential of hydroxyapatite as a carrier of bone morphogenetic proteins for post operative accelerated healing, and implant durability, the tailored microstructural properties, and protein adsorption capabilities of thin film hydroxyapatite implant surfaces were investigated.A novel particulate sol method was used to fabricate HAp thin films on bioinert glass, and Ti6Al4V substrates by dip and spin coating. The microstructural characterization of the thin films was carried out by SEM/EDX, AFM, XRD, and FTIR, and their surface roughness, Vickers hardness and adhesion strength were determined. The effects of silk fibroin and sericin thin film layers on the HAp film microstructure, and model protein (bovine serum albumin, BSA) adsorption behavior (by the size exclusion HPLC method) were investigated. The minimum threshold solid content of the suspensions was determined as 15% by weight for a continuous HAp film structure. The silk sericin and fibroin intermediate layers drastically improved homogeneity of the HAp layer. The BSA adsorption of the glass/sericin/commercial-HAp film was 2.6 ug/cm2, more than twice of the glass/commercial-HAp, and glass/sericin/dry-milled-HAp films, evidencing the effectiveness of surface micro/nano topographical structure as well as chemical structure. The XRD patterns of spin coated commercial-HAp films on Ti6Al4V pointed out to a particular crystal orientation which increased the positive degree of cooperativity between HAp and proteins during adsorption or deposition.