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Izmir Institute of Technology

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Browsing Izmir Institute of Technology by Subject "2D materials"

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    Master Thesis
    Functionalization and thickness dependent properties of single layer dichalcogenides
    (Izmir Institute of Technology, 2019-12) Kahraman, Zeynep; Şahin, Hasan; Akdoğan, Yaşar
    After successful isolation of graphene in 2004, it was found that the layered materials showed different properties when diluted to the monolayer. The layer dependent structural, electronic and vibrational properties of the 1T phase of two dimensional (2D) platinum diselenide are investigated by means of state-of-the-art first-principles calculations. In addition ultra-thin two-dimensional Janus type platinum dichalcogenide crystals formed by two different atoms at opposite surfaces are investigated by performing state-of-the-art density functional theory calculations. While all Janus structures are indirect band gap semiconductors as their binary analogs, their Raman spectra show distinctive features that stem from broken out-of-plane symmetry. Moreover, it was shown that vertically stacked van der Waals heterostructures of binary and ternary (Janus) platinum dichalcogenides offer wide-range electronic features by forming bilayer heterojunctions of type-I, type-II and type-III. On the other hands, Ab initio calculations are performed in order to investigate the structural, vibrational, electronic, and piezoelectric properties of both bare TaS2 and its functionalized structures. Furthermore, the elastic and piezoelectric properties of TaS2 and its derivatives are analyzed. It is revealed that the in-plane piezoelectricity of TaS2 can be enhanced via one-surface fluorination while an additional degree of freedom for the piezoelectricity can be added in all Janus structures due to the broken out-of-plane symmetry. This thesis provides some important results understanding of thickness and functionalization dependent mechanics, vibrational, electronic properties of 2D materials.
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    Doctoral Thesis
    Optical and electronic properties of atomically thin layered materials: First principles calculations
    (Izmir Institute of Technology, 2019-07) İyikanat, Fadıl; Senger, Ramazan Tuğrul; Şahin, Hasan
    The extraordinary interest in two-dimensional (2D) materials is increasing day by day. Thanks to advances in the experimental techniques, monolayer form of another material is synthesized every day with features not seen in the bulk form. Ab initio methods provide useful tools for characterizing and functionalizing the various properties of these materials. The results obtained through first principles quantum-mechanical calculations can help to predict and understand the experimental data, such as the position and source of the spectroscopic peaks in the Raman or optical absorption spectra. The aim of this thesis is to predict and functionalize the optical and electronic properties of atomically thin layered materials using density functional theory and approaches beyond. Within the scope of this thesis, possible technological applications of various 2D materials ranging from perovskite crystals to transition metal dichalcogenites are investigated by using several functionalization methods. In order to accurately predict the optical properties of these materials, it is very important to use approaches that take into account the many-body effects. Recent studies have shown that many-body perturbation theory in the form of GW approximation is highly reliable to calculate the quasiparticle properties of materials. By solving the Bethe Salpeter equation on top of GW calculation, the quasiparticle energies and excitonic properties, which have dominant effect in the optical properties of ultra-thin materials are examined in detail.