Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Author: search.filters.author.Balcı, Sinan

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  • Master Thesis
    Graphene-Like Materials for Electronic Applications
    (01. Izmir Institute of Technology, 2020) Başkurt, Mehmet; Şahin, Hasan; Balcı, Sinan
    Two-dimensional (2D) materials have gained vast interest in nanotechnology since these materials exhibit extraordinary properties due to electron confinement. Starting with graphene, many other 2D materials with characteristics of metals, semiconductors, insulators, and their magnetic analogues have been studied over the years. Insulators show importance as dielectric layers. Low dimensional metallic materials are used in electrical conduction. Ultra-thin semiconductors have variety of potential applications due to their characteristic band gap. Magnetic analogues of low dimensional materials are used in spintronics, offering high frequency, controllable switching. In addition, defects in these materials alter their physical properties and the concept can be adopted in order to use in different practices. Therefore it is important to study array of such materials and consider the alteration in their lattice theoretically and experimentally. In this thesis, first-principles calculations are used to predict insulating calcium halide single-layers are predicted, determine the effects of strain and V dopant in recently synthesized magnetic semiconducting VI3 single-layers, propose synthesis of magnetic, semiconducting manganese fluorides from manganese dichalcogenides, investigate the affects of defects and simulate scanning tunneling microscopy images in order to compare with experimental results, and finally to determine rather the detection of volatile organic compounds (VOC) such as methanol and ethanol by graphene-based sensors is feasible or not. Experiments are carried out to construct and further investigate the mechanism of VOC detection and working, highly sensitive alcohol sensors.
  • Master Thesis
    Flexible Transparent Conducting Electrodes Based on Silver Nanowire, Graphene, and Two-Dimensional Transition Metal Dichalgogenide
    (01. Izmir Institute of Technology, 2020) Tertemiz, Necip Ayhan; Balcı, Sinan
    In recent years, transparent conductive electrodes have attracted great interests owing to their critical applications in various optoelectronic devices, such as light emitting diodes, solar cells, liquid crystal displays, optical modulators, and touch screens. In this thesis, graphene-silver nanowires-transition metal dichalcogenide based hybrid transparent and conductive electrodes have been fabricated. In order to reach this goal; (1) single layer graphene on copper foil has been synthesized in large area in a CVD furnace, (2) ultrathin and very long silver nanowires have been synthesized by using wet chemistry methods, (3) MoS2 and WS2 single layer flakes and multilayer thin films have been synthesized in a CVD furnace, (4) electrodes of graphene, silver nanowires, and transition metal dichalcogenides have been fabricated on rigid and flexible substrates.
  • Master Thesis
    Investigation of Photodetectors Using Graphene Field Effect Transistors Incombination With Functional Dyematerials
    (Izmir Institute of Technology, 2020) Yakar, Ozan; Balcı, Sinan; Şahin, Hasan; Balcı, Sinan; Şahin, Hasan
    A J-aggregate dye is a type of water-soluble, functional dye, which has a sharp and narrow absorption peak after it self-assembles into a brick-wall structure at high concentrations. The absorption peak of the J-aggregates is sharp, narrow and shifted to longer wavelengths compared to their monomer form and it is in the visible or near infrared spectrum. Due to its very sharp and narrow absorption, it has been used in silver halide photography, non-linear optics, lasing and sensing applications. On the other hand, graphene is one atom layer thick, honeycomb lattice of carbon atoms. In the pure, freestanding form, the bands of its electronic structure touch at one point, making it a gapless semimetal. Due to this characteristic, it is possible to manipulate its optical and electronic properties by changing the Fermi energy of graphene. Therefore, graphene found applications in many fields such as light emitting diodes, photodetectors, Hall sensors, optical modulators and flexible optoelectronics. The functional dye materials have not been combined with graphene photodetectors even though they are highly sensitive to light, less toxic than their competitors and stable at room temperature. In this thesis, using a J-aggregate dye, which has a sharp absorption peak around 585 nm wavelength, a graphene phototransistor has been demonstrated. By changing the charge concentration on graphene, using the charge carriers that arise from the excitation of J-aggregate dye, reversible modulation of graphene Dirac point has been demonstrated. In addition, a novel thin film formation technique has been developed in this study. Porous polyethylene membrane has been used to create thin films of water-soluble materials, such as J-aggregates, on hydrophobic surfaces.
  • Master Thesis
    Plasmonic Enhancement of Perovskite Photoluminescence
    (Izmir Institute of Technology, 2020) Tan, Metin; Sarı, Emre; Balcı, Sinan
    Recently emerged perovskite materials show superior features like high efficiency, defect tolerance, facile synthesis, bandgap tunability and wide color gamut over their rivals in photonics applications. On the other hand, metals have interesting characteristics as they go smaller in size. Their absorption and scattering properties are completely different as nanoparticles. Their confined electron oscillations bring peculiar consequences. Due to change in these features, metallic nanoparticles can enhance or quench fields around them. Light-matter interactions determine how we see the world. Understanding quantum nature of light and matter and their interactions can benefit higher efficiencies and can open paths for novel technologies. In accordance with this purpose, this thesis study involves synthesis of cesium lead halide perovskite emitters and investigation of their interactions with silver nanoisland films. It was concluded that direct contact between perovskite layer and nanoislands results in a fluorescence quenching where intensity average lifetime decreases below 1 ns. Separating these layers with an alumina dielectric layer increased photoluminescence intensity after 15 nm and the highest intensity was observed at 18 nm thickness with 78% of PL enhancement. With different spacer thickness values, we achieved to see the change in photoluminescence intensity.
  • Master Thesis
    Experimental and Theoretical Investigation of Functionalized Perovskites
    (Izmir Institute of Technology, 2020) Özen, Sercan; Şahin, Hasan; Balcı, Sinan
    The last decade witnessed the rapid increase in the interest of the cesium lead halide perovskites (Cs-LHPs) and their successful applications in optoelectronic devices and photovoltaics. Increasing interest in perovskites arises from their extraordinary features such as having a tunable bandgap, variety in the crystal structure and phases, high photoluminescence quantum yield, ease of synthesis, and wide range absorption spectrum. Desiring to go beyond the emerging findings, subsequent studies have focused on the functionalization of perovskite nanocrystals (PNCs) by dimensional modifications and doping. This thesis study focuses on the modification of characteristics of Cs-LHPs by doping scenarios and dimensional reduction. Firstly, we reveal the modifications originated from the intercalation of Cr+3 and Gd+3 dopants into the Cs-LHP crystal structures. Cr+3 doping process is performed by using room temperature anti-solvent crystallization method. It is observed that the doping process leads to the emergence of distinctive signals in the PL spectrum. We clarify the origin of each additional PL peaks by experimental measurements and theoretical calculations. Additionally, white light emission is also achieved by the Cr3+ doping process. On the other hand, by using the hot-injection method, we synthesized neat and Gd+3 doped ?-CsPbI3 NCs. The stability of ?-CsPbI3 NCs is increased by the intercalation of Gd3+ ions into the host lattice. Also, enhancement of PLQY and lifetime is achieved by Gd3+ doping. Besides, to understand the dopant-induced modifications in the electronic and optical characteristics of perovskites, we also performed ab-initio density functional theory (DFT) calculations. In addition, we study how the characteristic properties of Cs-LHPs are modified upon dimensional reduction. By introducing the electrospraying method we reduced the synthesis and coating processes into a single step. Two-dimensional perovskite nanoplatelets were synthesized by electrospraying. We tuned the emission wavelengths of nanoplatelets in the range of 100 nm by thickness modifications. Lastly, by using DFT, we investigated the effect of thickness-dependent modifications on the structural, electronic, and vibrational properties of the orthorhombic CsPbI3 structure. Phonon calculations show that two ultra-thin forms of bulk CsPbI3 are dynamically stable. Also, the increase in the bandgap energy of the CsPbI3 structure by a decrease in thickness is revealed by electronic band dispersion calculations.
  • Master Thesis
    Dimension Dependent Optoelectronic Properties of Cesium Lead Halide Perovskites
    (Izmir Institute of Technology, 2019) Özcan, Mehmet; Şahin, Hasan; Balcı, Sinan; Şahin, Hasan; Balcı, Sinan
    All-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.