GCRIS

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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.
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.
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 Degree / Yüksek Lisans Tezleri

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