Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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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 Dimension Dependent Optoelectronic Properties of Cesium Lead Halide Perovskites(Izmir Institute of Technology, 2019) Şahin, Hasan; Şahin, Hasan; Balcı, Sinan; Şahin, Hasan; Balcı, Sinan; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyAll-inorganic cesium lead halide perovskites (ILHPs), are gaining wide variety of role as strong contenders due to their extraordinary photovoltaic features in optoelectronic research with tunable band-gap, large absorption cross-section, long carrier lifetime, and high carrier mobility. Most of the initial studies focused on bulk-like perovskite materials, while the rapidly growing colloidal perovskite nanocrystals impress additional interest because of their unique properties. In this thesis, colloidal lead halide perovskite nanocrystals’ optoelectronic properties are investigated and associated with their size and dimensionality. The photoluminescence characteristics of colloidal lead halide perovskite nanocrystals can be tuned by reducing their dimensionality. Thin layer fabrication of CsPbBr3 films which consist of 2D lead halide perovskite nanoplatelets, is achived by a novel coating approach via electrospraying from precursor solution. Electrospraying method represents not only a new and fast perovskite film fabrication but also dimensional tunability by changing the amount of oleylamine which is intercalating agent. Moreover, thicknessdependence of the structural, electronic and vibrational properties of orthorhombic CsPbI3, which is one of the most stable phase at room temperature, is investigated by means of state-of-the-art first-principles calculations. It is also investigated that the electronic band gap increases with decrease in perovskite thickness due to quantum size effect. Lastly, it is investigated that water induced transition to form large bundles of CsPbBr3 nanowires show a a redshifted photoluminescence. Water molecule causes the detachment of ligands from the perovskite surface which leads to form bundles. In summary, this thesis provides an understanding of dimension dependent optoelectronic properties of lead halide perovskite.Master Thesis Metamaterial antenna design for 5.8 GHz Doppler radar(Izmir Institute of Technology, 2018) Yılmaz, Hasan Önder; Yaman, Fatih; Yaman, Fatih; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThis thesis presents mainly simulation and measurement results of metamaterial based transmitter and receiver antennas for a Doppler radar system operating at 5.8 GHz and indoor, outdoor and through-wall performances of the Doppler radar system after the integration of field and the realized transmitter and receiver antennas. Firstly, the antennas are modeled via 3D electromagnetic simulation program CST:Microwave Studio and related parameters are calculated. Afterwards, in order to observe antenna performances, radiation pattern and gain characteristics of realized antennas are measured in laboratory environment including anechoic chamber. Another essential objective of this thesis is to examine and analyze applicability and effectiveness of the metamaterial based antennas for a 5.8 GHz Doppler radar system. For this reason, a double negative index metamaterial structure is integrated to a patch antenna for the transmitter. For the receiver antenna, a near-zero index medium is designed to locate over patch antenna. Accordingly, significant improvements in size and bandwidth for the transmitter and in gain and directivity for the receiver in addition to improvement of its psychical size are obtained. It is shown that return loss, radiation pattern and gain measurement results of the designed antennas agree well with the simulations for a desired frequency band. According to the experimental data, the realized transmitter antenna has a higher directivity value as compared to the simulated one, therefore it radiates most of the power into narrower area. Additionally, the measured one has a wider bandwidth. The measurement results of receiver antenna are consistent with simulation in terms of bandwidth, return-loss, radiation pattern of horizontal direction and gain value. The last part of the thesis is devoted to expressing the application of the designed antennas to the low-power, short-range Doppler radar system, which is designed to detect the speed of the human or moving target in the indoor/outdoor environment or behind the wall. Improvements on the performance of the radar system integrated with metamaterial antennas are discussed and performances results are commented.