Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Lead-Free Ferroelectric Ceramics for Energy Storage and Electrocaloric Cooling Applications(01. Izmir Institute of Technology, 2022) Karakaya, Merve; Karakaya, Merve; Adem, Umut; Adem, UmutThis thesis study consists of five main chapters that include an introduction about the principles and applications of ferroelectrics and four chapters on different lead-free ferroelectric ceramic systems developed for the energy storage and electrocaloric cooling applications. In the first chapter, the principles of ferroelectricity and dielectric, piezoelectric and pyroelectric properties of ferroelectrics are introduced followed by the applications considered in this thesis: Electrocaloric cooling and capacitive energy storage. In the second chapter, the effects of bismuth lithium titanate incorporation into sodium bismuth titanate-barium titanate systems on the energy storage properties have been discussed. In addition, it has been calculated that these compositions have improved energy storage properties close to the high values obtained in the literature. In the third chapter, the effect of two different manganese precursors on the probability of defect dipole formation, ferroelectric aging and resulting manganese valences of ceramics were investigated by manganese doping on barium strontium titanate base ceramics. In addition, their electrocaloric properties were investigated by indirect method. In the fourth chapter, electrocaloric properties of barium titanate - sodium bismuth titanate systems has been investigated. The increase in tetragonality by sodium bismuth titanate incorporation has been verified by Rietveld refinement and those compositions were shown to be suitable for electrocaloric applications. In the fifth chapter, a sodium bismuth titanate - potasium bismuth titanate composition which is in morphotropic phase boundary, was synthesized by templated grain growth method, and the effect of orientation on the electrocaloric effect was investigated by direct and indirect measurements.Doctoral Thesis Biological Nano Silica Reinforced Polymeric Composites(01. Izmir Institute of Technology, 2022) Ülker, Sevkan; Güden, MustafaThe present thesis study focused on processing nano-silica powders of varying sizes and crystallinities through heat treatment (900–1200 °C), hydrofluoric acid leaching (1–7 N), and ball milling (1 h, 500 rpm) of natural diatom frustules. As-received frustules was composed of amorphous silica (88%) and quartz. The partially ordered crystalline low-quartz and/or precursor to low-cristobalite started to form at ~900 °C. As the heat treatment temperature increased, the crystallinity of the frustules increased from 9.3% at 25 °C to 46% at 1200 °C. Applying a ball milling reduced the mean particle sizes of the as-received and heat-treated frustules from 15.6–13.7 μm to 7.2-6.7 μm, respectively. Acid leaching of the as-received and heat-treated frustules resulted in a further increase in the crystallinity. Furthermore, ball milling applied after an acid leaching was very effective in reducing the particle size of the as-received and heat-treated frustules. The mean particle size of the acid-leached frustules decreased to 774-547 nm with a crystallinity varying between 12 and 48% after ball milling. A partially dissolved amorphous phase was observed in between crystalline silica grains after acid leaching, which resulted in a rapid fracture/separation of the frustules in ball milling. The prepared nano-silica powders were further used as a filler in an epoxy matrix. The tensile strength, fracture strain, and modulus of epoxy increased with increasing the volume percent of nano-silica up to 2%. The increase in the yield strength and elastic modulus was about 50% and 30% with the addition of 2 vol% frustules, respectively. The rule of mixtures showed a very good agreement with the experimental elastic modulus values and a numerical model of the tensile test in LS-DYNA agreed well with the experimental tensile stress-strain behavior. The microscopic observations showed the presence of nano-silica powder, proving an efficient load transfer from matrix to powders on the fracture surfaces, confirming a strong interface between silica powders and matrix.Doctoral Thesis Development of Novel Anticounterfeiting Technologies Using Heavy Metal Free Nanoparticles(Izmir Institute of Technology, 2021) Taşcıoğlu, Didem; Özçelik, Serdar; Demir, Mustafa MuammerCounterfeiting, the act of illegally copying a product, document or currency, is a growing problem and causes economic losses. Anticounterfeiting technology uses fluorescent inks that are invisible to the naked eye in daylight, but become visible under UV light. However, these inks have problems such as fading when exposed to sunlight or room light for a long time and disappear completely over time. This is due to the relevant inks are made using organic dyes that fade. The inks used in anticounterfeiting application preventing copying of secure documents such as banknotes, passports and ID cards must be health-friendly and chemically and optically stable for years. All of the existing security materials and equipments for ID cards, driver's licenses, passports, banknotes used in our country are imported. In this study, our aim is to create a new generation of security materials and codes to combat counterfeiters and to verify the generated security codes in a simple, efficient and fast way. In this study, it is aimed to produce nanoparticles, which do not contain heavy metals and show optical stability for a long time, emitting in visible region, on the basis of the security codes created. For this purpose, water and solvent-based nanoparticles synthesized which are non-toxic should have a long-term optical stability. The synthesized nanoparticles act like a pigment in security codes. The photoluminescence (emission color) of the security codes can be adjusted by size and chemical composition of nanoparticles. In this study, colloidally monodispersed and highly photoluminescent InP based nanoparticles were synthesized by the hot-injection approach under an inert atmosphere. In addition, a protective shell (ZnS, ZnSe) coating methods have been applied to provide optical stability to InP nanoparticles. Moreover, carbon-based nanoparticles with high optical stability and being dispersible in water were synthesized using the bottom-up method. Security codes that cannot be detected in daylight have been created on different subtrates (paper, polymer, glass, etc.) by using screen printing and inkjet printing methods, which are well known printing methods using the synthesized nanoparticles. In addition, the authenticity of the security codes was checked using a commercial fiber optic based spectrometer (Ocean Optics spectrometer) and a handy hand-held optical device called the Quantag sensor developed by Quantag Nanotechnologies. Thus, a verification method that can be distinguished by a simple detection device is proposed. The synthesized nanoparticles were furthermore dispersed in a polymer solution to create random droplet and droplet/fiber patterns by electrospinning method. Thus, unique and inimitable security codes detectable under UV light were created which may be used in the fight against counterfeiting. To check the authenticity of the original security codes created; images collected with a simple smartphone microscope and a database was created in which the original patterns were recorded. The originality of the random patterns obtained was checked by comparing it with the patterns recorded in the database. In addition, the spectral information of the particle from the droplet/fiber pattern obtained was determined with a simple hand-held device (Ocean Optics optical spectrometer). Thus, by reading spectral information from the pattern, the spectral signature of the nanoparticles was determined and thus a second-step security was created. In this way, a two-stage anticounterfeiting technology that is impossible to imitate has been developed. As a conclusion, it is believed that the security codes developed in this study will pave the way for the commercialization of quantum labeling technology.Doctoral Thesis Terahertz Imaging Applications and Characterization of Ito Thin Films Grown by Magnetron Sputtering(Izmir Institute of Technology, 2020) Köseoğlu, Hasan; Özyüzer, LütfiTHz 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 Development of Plasmonic Nanostructures for Photothermal Therapy of Prostate and Breast Cancer(Izmir Institute of Technology, 2019) Tomak, Aysel; Bulmuş, Volga; Şahin, HasanThe aim of this thesis is to synthesize gold nanorods (AuNRs) and lipid-stabilized nanobubbles containing AuNRs and investigate the potential of these plasmonic nanostructures as photothermal therapy agents for breast and prostate cancer through in vitro cell culture experiments. For this aim, firstly, AuNRs were synthesized at varying aspect ratios (ARs) and characterized via several techniques including UV-Vis/NIR spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), inductively coupled plasma-mass spectroscopy (ICP-MS), electrophoretic light scattering (ELS) and X-ray photoelectron spectroscopy (XPS). The surface of AuNRs was modified with a biocompatible polymer, poly(ethylene glycol) (PEG), via ligand exchange method. Cytotoxicity, cell uptake and photothermal effects of AuNRs were investigated via in vitro cell culture experiments using human prostate cancer (DU 145) and epithelial (RWPE-1), breast cancer (MCF7) and epithelial (MCF 10A) cell lines. It was concluded that AuNRs (AR=4.0) were superior than AuNRs (AR=7.0) in terms of cell viability and photothermal effect. Separately, a non-commercial antibody (Ab) targeting a specific sialic acid derivative on the plasma membrane of DU 145 and MCF7 cancer cells was conjugated to AuNRs. Conjugations were characterized with the same techniques and investigated via in vitro cytotoxicity and cell uptake experiments. The Ab-conjugated AuNRs displayed the capability of selective targeting prostate cancer cells. Additionally, lipid-stabilized AuNRs and lipid-stabilized nanobubbles containing AuNRs (AuNBs) were synthesized for the first time and characterized using UV-Vis/NIR spectroscopy, SEM, ICP-MS and ELS techniques. Lipid-stabilized AuNRs were successfully synthesized using varying lipid mixtures instead of cationic, toxic surfactant. Separately, AuNBs were synthesized by combining PEG modified AuNRs with DPPC: DSPE-PEG lipid film under sonication and gas stream. AuNBs showed the same or significantly lower toxicity depending on the cell types and the same photothermal effect with respect to AuNRs (AR=4.0) upon irradiation under laser at 808 nm.Doctoral Thesis Single-Photon Generation From Defects and Manipulation With Nanostructures(Izmir Institute of Technology, 2019) Özçeri İyikanat, Elif; Aygün, Gülnur; Tarhan, Enver; Tarhan, Enver; Aygün Özyüzer, GülnurSingle-photon sources are essential components for several applications in the field of quantum information technologies, such as quantum cryptology and quantum computation. To this aim, efficient generation and detection of single-photons are the crucial to be achieved. Among single-photon sources that are extensively studied in the literature, defect centers in solid are very promising due to their room temperature operation and their stability. The aim of this thesis is to generate single photons at room temperature and control their optical properties by nanostructures. Single-photon emission from TMDCs originates from localized weakly bound excitons at cryogenic temperatures due to their small exciton binding energies. However, room temperature SP emission from WS2 can be obtained by creatingWO3 defects. In our study, room temperature emission from defects in WO3 was investigated. Density functional theory calculations showed that the source of the emission can be oxygen defects. Additionally, the emission was brightened by plasmonic gold nanoparticles. Furthermore, defects in two-dimensional (2D) hexagonal boron nitride (hBN) is offered as an efficient room temperature SPS. HBN is a wide bandgap 2D material, in which defect centers create discrete energy level to generate single photons. In our study, reversible single-photon emission control from defects in hBN was demonstrated by Förster-like resonance energy transfer between the single-photon emitter and a graphene layer. To this aim an ionic liquid based device structure was used.Doctoral Thesis Magnetic Effect in the Biological Functioning of Hemoglobin: Dft+qmc Approach Within an Effective Multi-Orbital Anderson Impurity Model(Izmir Institute of Technology, 2019) Mayda, Selma; Bulut, Nejat; Demir, Mustafa MuammerHemoglobin corresponds to O2 transportation from lungs to the tissues and exhibits high-spin to low-spin transition by binding of O2 to Fe. In this thesis, we study the electronic and magnetic properties of the deoxy and the oxy forms of the human adult hemoglobin (HbA) to investigate the mechanism of the spin transition. We use an effective multi-orbital Anderson model and the parameters of this model are determined by the density functional theory (DFT) calculations. Then, this model is solved by using a quantum Monte Carlo (QMC) algorithm. The DFT+QMC results show that new electronic states named as the impurity bound states (IBS) exist in both deoxy-HbA and oxy-HbA.We also observe that as the temperature decreases, a magnetic gap is opened at the Fermi level for oxy-HbA. This gap arises from the Fe-O2 charge transfer. We find that both the IBS and the opening of the magnetic gap are responsible for the spin transition in hemoglobin. In addition, the DFT+QMC calculations show that antiferromagnetic (AF) correlations between the Fe(3d) and the surrounding orbitals exist in both deoxy-HbA and oxy-HbA. For deoxy-HbA, the anomalous magnetic circular dichrosim signal in the UV region is experimental evidence for these AF correlations. In the light of these magnetic measurements, we propose some explanations for the Bohr effect and the cooperativity which are the fundemental functional properties of the hemoglobin. The results presented in this thesis show that the magnetic effects play a crucial role in the funtioning of the hemoglobin.Doctoral Thesis Processing Foam-Like Porous Glass Structure Using a Combined Process of Glass Powder Expansion in Aqueous Environment and Sintering Process(Izmir Institute of Technology, 2019) Zeren, Doğuş; Güden, Mustafa; Akdoğan, YaşarSoda-lime glass foams were formed by the controlled pore structure of inorganic particle-liquid suspensions at room temperature and then sintered at elevated temperatures between 650oC-800 oC. The slurries were prepared using the glass particles below 38 µm (fine), between 38 and 45 µm (medium) and between 45 and 56 µm (coarse) and with 50, 55, and 60 wt% solid content and 2, 3, and 4 wt% carboxymethyl cellulose (CMC) binder addition. The slurries were foamed using an Al-based foaming agent and a calcium hydroxide alkali activator with an amount of 1 wt%. An increase in CMC content and a decrease in particle size shifted the slurries from a Newtonian to a non-Newtonian behavior and slurry stabilization with the CMC addition. The extensively increased initial bubble pressure in high viscosity slurries resulted in higher linear expansion rate initially followed by a bursting of gas bubbles. The maximum foam linear expansion of the slurries increased with CMC addition until about ~5 Pa s and the expansions stayed almost constant over 400% expansion, while the slurries with the viscosity above 50 Pa s could not be foamed. The most effective factor on the maximum expansion was found the solid content followed by CMC content and the least effective factor was determined the particle size. Partial bonding of glass particles and excessive shrinkage of glass particles due to the melting of foam green bodies were seen at 650 and 800 oC sintering temperatures. Prepared foam glasses showed lower compressive strengths and thermal conductivities than the glass foams reported in the literature. Finally, foaming at room temperature with this technique was found to be more advantageous than conventional glass foam production techniques due to ease of pore formation controlling at room temperature.Doctoral Thesis The Fabrication of Plasmonic/Photonic Nanostructures in Polymers: Mechanical Sensor Applications(Izmir Institute of Technology, 2019) Topçu, Gökhan; Demir, Mustafa Muammer; Eanes, MehtapFunctional polymer nanocomposites offer futuristic properties by the association of inorganic additive micro-/nanostructures into the polymers. With the growing knowledge of the physical fundamentals, stimuli-responsive polymeric composites enable detection of chemical, thermal, and mechanical changes by optical sensors and probes. Since the accurate real-time detection of the change in mechanical loading is vital for construction and industrial fields, the use of colorimetric pressure elements in a static body is important for the prediction of catastrophic failures. In this thesis, strain/pressure responsive colorimetric films were produced. A number of polymer nanocomposite-based mechanical sensors are presented. By transferring the optical activity (coherent reflection and plasmonic coupling) of the additives into various polymeric matrices having different mechanical features, the strain and pressure sensors are developed for practical applications. There are two approaches used for the fabrication of polymeric mechanical sensors: i) PDMS/SiO2 composites, ii) PAAm/Au NP composites. The coherent reflectivity of SiO2 colloidal particle arrays was used to develop strain sensors while controllable localized surface plasmon resonance of Au NPs was employed for pressure sensors. These optical systems were separately associated with viscoelastic and elastic polymeric systems, and sensor properties were discussed.Doctoral Thesis Separation of Macromolecules From Aqueous Systems Using Electrospun Fibers(Izmir Institute of Technology, 2018) Işık, Tuğba; Demir, Mustafa MuammerElectrospinning has been recognised as a versatile method for the fabrication of continuous polymeric fibers with various type of morphology. Since it allows changing the fiber diameter, surface morphology and porosity by adjusting the solution and instrumental parameters, electrospun fibers present a wide range of properties that cannot be found in bulk materials. Through this thesis, removal of several types of pollutants from the aqueous systems was studied by using the electrospun fibers fabricated from both virgin and waste polymers. The first part of the dissertation deals with the removal of macromolecular pollutants from aqueous systems by using waste-based electrospun fibers. Electrospun fibers fabricated from CD cover and expanded polystyrene wastes were utilized for the protein-rich medical waste treatment by using Bovine Serum Albumin, Myoglobin and Trypsin as protein models. Electrospun fibers from expanded polystyrene wastes were utilized for the remediation of oily wastewaters. The second part of the dissertation deals with the polyatomic nuclear waste removal using uranyl ions as analyte and amidoxime functionalized PIM-1 electrospun fibers. The last part of this dissertation describes an approach for the fabrication of fluorine-free hydrophobic surfaces by electrospraying of methacrylate based linear and hyperbranched copolymers.