Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
Browse
8 results
Search Results
Master Thesis Colloidal Plexcitonic Nanocrystals(Izmir Institute of Technology, 2022) Sarısözen, Sema; Yalçın, Şerife HanımNoble metal nanocrystals, especially gold and silver, which have attracted a great deal of attention due to the supporting of surface plasmon polaritons (SPPs), have been extensively investigated and studied. With recent developments in colloid chemistry, synthesis of noble metal nanocrystals with tunable optical properties in the visible region of the electromagnetic spectrum has become easier. Until now, noble metal nanocrystals (NPs) synthesized by using various synthetic methods, have a variety of shapes, such as bipyramid, rod, disk, prism, and ring, etc. In the strong coupling regime, SPPs supported by metal nanocrystals interact strongly with excitons of organic dyes, semiconducting quantum dots (carbon or perovskite quantum dots) to generate a new hybrid optical mode called plexciton (plasmon-exciton). Plexcitonic nanocrystals have received interest owing to their ease of synthesis, scalability, and ability to provide sub-wavelength confinement of incident light and offer promising applications. Plasmon–exciton interaction at nanoscale dimension can be improved by generating new plexcitonic nanoparticles with tunable optical properties, which may be utilized in critical applications such as nanolasers, sensors, nano-optics, solar cells, and light emitting diodes. Therefore, there has been a tremendous amount of interest in the synthesis of new plexcitonic nanocrystals having excellent optical and chemical properties. The main goal of this thesis is to synthesize new plexcitonic nanoparticles with tunable optical properties in the visible spectrum: (i) synthesis of different shaped colloidal monometallic and bimetallic nanocrystals, (ii) synthesis of new colloidal plexcitonic nanocrystals, (iii) synthesis of carbon quantum dots (CDs), (iv) coupling of excitons of CDs and SPPs on the silver thin film.Master Thesis Development of Fluorescent Carbon-Dots for Biological Imaging(01. Izmir Institute of Technology, 2021) Kavuranpala, Tuğçe; Özçelik, SerdarCarbon dots are called carbon quantum dots or carbon nanoparticles (NPCs), and their use has recently started to increase thanks to their good biocompatibility, unique optical properties, easy synthesis, and low toxicity. Different kinds of carbon sources and amine sources also used as different dopes of chemical create a different emission color of CDs under UV-lamp. In this study, our aim to provide a simple synthesis of carbon dots with high quantum efficiency and low toxicity for use in cell imaging. Nitrogen and sulfur-doped carbon dots were synthesized using citric acid and thiourea, and emission was obtained in the blue-green region. After the synthesized carbon dots were seeded to the A549 cell culture, intracellular viability and cell toxicity results showed that carbon dots did not affect cell viability at certain concentrations. Afterward, the carbon dots are combined with gold nanoparticles and it is aimed to attach the gold to the surface of the carbon dots. Our aim here is to increase the efficiency of carbon dots, which give an emission peak at 550 nm, thanks to gold nanoparticles. As a result of these studies, it was proved by DAPI staining that the carbon dot is directed to the nucleus of the cell. Since it does not create a toxic effect and is transported to the cell nucleus, it allows it to be used in intracellular drug transport and imaging processes in the next stages.Master Thesis Photophysical Characterization of Green and Blue Emitting Quantum Dots and Their Application in Qd-Leds(01. Izmir Institute of Technology, 2020) Özgüler, Şahika; Varlıklı, CananQLED device construction and characterization studies were carried out in which QD nanoparticles synthesized within the scope of TÜBİTAK project no 115F616, and were used as emission layer. By examining the photo-physical and morphological properties of films prepared with the use of quantum dot (QD) nanoparticles, quantum dot light emitting diodes (QLEDs) which are one of the fields of molecular electronics, were applied as an emission layer using the spin coating technique from wet coating processes. The photo-physical and morphological characterizations of the solution and film phase of blue and green emitted QD nanoparticles were made. For the QDs, the concentration difference in the solution phase was characterized and its effects on film properties were investigated. It has been determined that the increase in concentration does not have a dramatic effect on photo-physical properties but seriously affects film thickness and surface roughness. In this case, performance of blue and green light emitting quantum dot diodes (QLED) prepared by the spin-coating technique, where each QD film is used as the emission layer, have been investigated.Master Thesis A Computational Study of Excitation Dynamics on Semiconductor Surfaces(Izmir Institute of Technology, 2019) Kaya, Birnur; Sevinçli, Haldun; Özçelik, SerdarRecent experimental studies have shown that collodial quantum dots can be produced in large quantities and their optical properties can be tailored by controlling their composition, size and surface characteristics. Motivated by these studies, this thesis is devoted to the investigation of excitation dynamics on semiconductor surfaces, which are passivated with organic molecules. First, constructing a simplified model, excitation dynamics is investigated by computing time dependent occupations of frontier molecular orbitals for various scenarios regarding the values for the energy gap between the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO), as well as the coupling strengths. Second, the model is enhanced to address realistic systems. Passivation of ZnS surface with oleic acid (OA) is modeled using density functional theory based tight binding (DFTB) simulations. Extracting the Hamiltonian and overlap matrices, excitation dynamics is studied for Zn rich and S rich surfaces and different coverage ratios of surfaces. The excitation dynamics is compared and contrasted against the simplified model. Characteristic features are identified and typical decay rates are calculated for various molecular configurations. In addition to these, X-Ray diffraction spectra of quaternary ZnCdSSe nanoalloys have been investigated.Master Thesis Development of Copper and Manganese Doped Ternary Colloidal Quqntum Dot Alloys(Izmir Institute of Technology, 2019) Yırtıcı, İlayda Melek; Özçelik, SerdarSemiconductor nanocrystals have great interest due to their unique optical properties such as the particle size and the alloy composition dependent spectra, photochemical and colloidal stability. They have wide range of potential applications like solar cells, light emitting diodes (LED) and bioimaging etc. In this thesis, colloidal ternary Cu doped and undoped ZnSxSe1-x nanoalloys were synthesized by modified one pot aqueous approach. TGA and MPA ligands were used as capping agents for the synthesis of ZnSxSe1-x and Cu doped ZnSxSe1-x colloidal nanoalloys. The results showed that capping agents have an significant effect on optical properties of ZnSxSe1-x nanoalloys. Although the TGA capped nanoalloys have well-defined absorption bands rather than MPA capped ones, ZnSxSe1-x nanoalloys with TGA capping agent fluorescence peak was not observed. Therefore, the further study was continued with MPA capped ZnS xSe1-x ternary nanoalloys. Optical spectra demonstrated both absorption and PL spectra were shifted due to the adding of Cu dopant. Absorption peak shifted from 335 nm to 376 nm. Fluoroscence spectra also was redshift from 469 nm to 565 nm. Thus, we can conclude that, colloidal ternary nanoalloys optical properties can be tuned by using chemical doping. On the other hand, the optical and structural properties of binary ZnSe QDs, Mn and Cu doped ZnSe nanocrystals were investigated. We concluded that ZnSe and ZnS xSe1-x nanocrystals can be used to synthesize doped nanocrystals by chemical doping. We demonstrated that optical and structural properties of Cu and Mn doped ZnSe can be tuned by chemical doping.Master Thesis Development of Semiconductor Nanocrystals for Biotechnological Applications(Izmir Institute of Technology, 2008) Ünlü, Caner; Özçelik, SerdarSemiconductor nanocrystals are very useful tools in biological applications because of their unique optical properties. In this study, synthesis and characterization of CdTe / CdS and CdSexS1-x nanocrystals were carried out. CdSexS1-x nanocrystals were synthesized by a modified two phase method. Highly luminescent (Quantum yied . %80) , monodisperse and face centered cubic CdSexS1-x nanocrystals were obtained in toluene. The size of nanoparticles varies from 3.5 to 3.7 nm Ligand exchange was performed on CdSexS1-x nanocrystals and luminescent water soluble CdSexS1-x nanocrystals were obtained. CdTe / CdS nanocrystals were synthesized in one step and and one pot by a modified method. Face centered cubic, luminescent (Quantum yield . 30%) and monodisperse CdTe / CdS nanocrystals with different sizes in a size range from 4.7 to 9.3 nm were obtained in water. Toxicity of CdTe / CdS nanocrystals was determined by MTT test. The lethal concentrations were respectively 1.0 and 15 .g/ml for PC3 and MCF7 cells. Confocal microscopy shows that the nanoparticles enter to the cytoplasm of cells.Master Thesis Synthesis, Characterization of Cdsxse1-X Quantum Dots and Evaluation of Their Real-Time Motions in Live Cells(Izmir Institute of Technology, 2011) Ünal, Gülçin; Özçelik, SerdarThe use of quantum dots as fluorescent labels in bioimaging is the most intensively studied subject. The aim of this study is to elucidate locations of quantum dots and track their motions in real time through confocal microscopy and to evaluate influence of surface chemistry on diffusions of quantum dots in live cells. In this study, trioctylphosphine oxide (TOPO) capped CdSxSe1-x quantum dots were synthesized and then TOPO molecules were exchanged with 3-mercaptopropionic acid and N-acetyl-Lcysteine to make quantum dots water dispersible for cellular imaging. Human lung adenocarcinoma epithelial cells (A549) and human bronchial epithelial cells (BEAS-2B) were incubated 1 hour with CdSxSe1-x quantum dots with a concentration range of 1-10 g/mL. Localizations and real time motions of quantum dots were tracked by a spinning disc confocal microscope. The center of fluorescent spots of quantum dots was determined by 2D Gaussian fitting with a sub-pixel resolution (<100nm/pixel). The mean square displacements, diffusion coefficients and trajectories in which quantum dots made motions were analyzed by the software ImageJ with a plug in Spot Tracker. Confocal images showed that both MPA and NAC cappped quantum dots were observed in the cytoplasm of cells. Trajectories of quantum dots in cellular environment demonstrated that the quantum dots performed various types of motions in live cells. Unimodal, trimodal and multimodal distribution histograms of the diffusion coefficeints were obtained for different capping agents (MPA and NAC) and cell types (A549 and BEAS-2B). We conclude that the surface chemistry regulates the motion of the quantum dots in the cellular environment.Master Thesis Excitonic Luminescence in Spherical Core-Multi Quantum Dot Structures(Izmir Institute of Technology, 2011) Bacaksız, Cihan; Senger, Ramazan TuğrulIn this thesis, we studied excitonic light emission from core-multishell semiconductor hetero-nanocrystals having a spherically symmetric shape as a function of core size and shell thicknesses. Different combinations of semiconductors were considered in the core/shell/shell structure. The multilayer quantum dot structures that we considered were in A/B/A/B form, where A and B denote II-VI binary semiconductor crystals. We used method of finite differences to solve the Schrödinger equation of the confined exciton problem numerically. Several approximations including the effective mass approximation for the electron and hole masses, and treatment of Coulomb interaction as a perturbation, were employed. Normalized oscillator strengths for optical transitions and coexistence of multiple transitions from a single structure at several frequencies have been investigated. In this study, three different pairs of semiconductors are considered. One of them is (CdSe) ZnS) CdSe) ZnSe), other is (CdSe) CdS) CdSe) CdSe) and third one is (CdTe) ZnS) CdTe) ZnSe). According to our calculation, (CdSe)ZnS)CdSe)ZnSe) structure, when the core radius is 1.51 nm with some different shells combinations, has multi-color emissions from higher frequency to lower frequency in the visible spectrum. (CdSe) CdS) CdSe) CdSe) structure has multi-color emissions when the core radii are 2.02 nm and 2.52 nm yet this structure is the most inefficient structures which we analyse Moreover, multi-color emissions are obtained from the structure (CdTe) ZnS) CdTe) ZnS) when the core radii are 1.29 nm, 1.93 nm, 2.58 nm and 3.23 nm. Also, this structure has nearly white light emission for 3.23 nm core radius with 3 ML ZnS shell and 1 ML CdTe shell, and with 4 ML ZnS shell and 1 ML CdTe shell.