Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Identification of Single-Layer Crystalline Structures Through Their Electronic and Optical Properties(01. Izmir Institute of Technology, 2021) Sözen, Yiğit; Şahin, Hasan; Balcı, SinanA large number of two-dimensional (2D) van der Waals type materials have become a focus of interest in many scientific fields, ever since the thinnest carbon compound, graphene, takes to the stage with its exceptional electronic properties. The outstanding electronic behavior resulting from quantum size effects requires an investigation of the electronic and optical features of materials at the atomic scale. The understanding of such properties of matter within the framework of the theoretical approaches is the first step to shed light on the discovery of electronic and optoelectronic devices including brand new features. This thesis discusses the identification of electronic and optical properties of several types of atomically thin crystals, consisting of 2D and lead-free perovskite structures, by means of density functional theory (DFT). In the first study, primarily, the strong interaction mechanism between Ge atom and single-layer GaAs was studied starting from single atom adsorption to detached germanene layer formation. Following that dynamically stable metallic structures of Janus and alloy type GaGeAs crystals are discovered by performing one-sided and alternated decoration of GaAs single-layer with Ge atoms, respectively. %The Raman spectroscopy is found to be applicable for phase detection as the theoretically calculated Raman spectra of each polytype exhibit distinctive signals. In the second study, bulk and dynamically stable ultra-thin structures of lead-free CsMnCl$_3$ are discussed. According to total energy and electronic band structure calculations, bulk, bilayer, and single-layer structures of CsMnCl$_3$ are robust antiferromagnetic insulators. In third and fourth chapters are devoted to the identification of different stacking types of GaP/GaSe heterobilayers, and two different hexagonal phases of single-layer Germanium Oxide by means of electronic and optical characterization tools, respectively. In these studies, for the purpose of providing an accurate solution for the prediction of absorption, reflectance, and transmission spectra of materials, excitonic effects are considered by employing Bethe-Salpeter formalism following the $G_0W_0$ approximation. Wide range of atomically thin crystal structures studied within the framework of this thesis are verified to be promising candidates for the development of future nano-sized electronic and optoelectronic device applications thanks to their attractive electronic and optical properties arising from strong quantum confinement effects.Master Thesis Modeling of Collection of Non-Spherical Particle Assemblies by Liquid Droplets Under Potential Flow Conditions(Izmir Institute of Technology, 2006) Selvi, İlker; Doymaz, FuatA model, which explains the collection of non-spherical particle assemblies by liquid droplets, was constructed. The system was investigated under potential flow conditions. It was possible to generate the streamlines around the particles and droplets via potential flow theory. Therefore, the complexity coming from eddies and vorticity was eliminated. Non-spherical particles and agglomerated particles were modeled using equivalent diameter assumption due to the boundary layer, rotation, and oscillation behaviors of the particles. Collection probability was calculated as a function of three different collection mechanisms: collision, adhesion, and engulfment. The interaction forces between particles and droplets were divided into two groups as external and internal forces. The gravitational force and the drag force due to the uniform flow rate caused collection mechanisms. Van der Waals and Electrostatic interactions were investigated in order to explain adhesion and wetting mechanisms. Through simulations, we have found that particle and droplet diameters were the most influencing parameters on the collision mechanism. The engulfment possibility could be increased by adding surfactant to the liquid solution. The results of this model showed similarities with the other models in the literature, as well as with that of the experimental studies.