Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
Browse
2 results
Search Results
Master Thesis Theoretical Investigation of Structural, Vibrational, Electronic, and Elastic Properties of Ultra-Thin Anisotropic Materials(01. Izmir Institute of Technology, 2024) Doğan, Kadir Can; Yağmurcukardeş, Mehmet; Ateş, SerkanDimensional reduction in materials leads to significant improvements and changes in various properties due to quantum phenomena and intense confinement of electrons. Since the separation of graphene from bulk graphite in 2004, many different materials with layered bulk structures have been experimentally introduced into the literature, including hexagonal boron nitride (BN), transition metal dichalcogenides (TMDs), and in-plane anisotropic monolayer black phosphorus (BP). Among ultra-thin materials, anisotropic materials have attracted attention due to their distinct orientation-dependent vibrational, electronic, optical, and mechanical features and have been shown to have high potential for special applications such as polarization-sensitive photodetectors, orientation-dependent optoelectronic devices, and orientation-sensitive sensors. The aim of this thesis is to predict the stable structures of ultra-thin anisotropic materials such as HfTe5, TiX5, TaX3 (X:S, Se, Te), bismuthene and magnetic MnPS3 nanoribbons and to understand their structural, magnetic, vibrational, electronic, optical and elastic properties on a physical basis by performing density functional theory (DFT)-based first-principles calculations. Preliminary data via STM images are presented for the potential experimental characterization of possible defects and oxidized structures of the single-layer HfTe5, whose predicted stable structure. The existence of stable structures of titanium-based penta-calcogenides is predicted and the direction-dependent properties of the stable phases are investigated. The dynamic stability of Ta-based trichalcogens exhibiting anisotropy different from TiS3 and ZrS3 has been investigated and their crystal-orientation dependent elastic properties are analysed. In addition, in the tilted α-bismuth known as the α phase, the identification of the external strain direction through the Raman spectrum is examined. The reduction of in-plane anisotropy to 1 dimension is studied through the edge type- and width-dependent properties in magnetic MnPS3 nanoribbons. Our findings are important for the prediction of novel anisotropic materials.Master Thesis Dark Energy Mechanisms in the Context of Extra Dimensional Models(Izmir Institute of Technology, 2011) Yağmurcukardeş, Mehmet; Erdem, RecaiDark energy is the simplest and the most standart explanation to account for the observed accelerated expansion of the universe. In this thesis we use the term 'dark energy' in its standart meaning i.e. a field or fluid that is responsible for the cosmic acceleration in the frame work of general relativity. Meanwhile extra dimensions is an attractive framework to understand many otherwise unexplained physical phenomena in a clear, simple formulation. Therefore the study of extra dimensional cosmological models is an attractive area of study. In this thesis we have considered viability of extra dimensional cosmological models in the light of the accelerated expansion of the universe. We have confirmed the results of studies that have shown the incompatibility of a broad class of extra dimensional cosmological models with a dark energy of an equation of state close to that of cosmological constant. We have discussed also possible theoritical and vational ways to avoid the no-go theorems for extra dimensional cosmological models as well.