Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Utilization of Graphene and Mos2 for Volatile Organic Compound Sensor Applications(01. Izmir Institute of Technology, 2023) Duran, Tuna; Büyükçakır, Onur; Şahin, HasanThe novel 2D materials such as graphene and transition-metal dichalcogenides have already shown impressive volatile organic compound (VOC) gas monitoring performances as in sensitivity, limit of detection and response time. This thesis discusses the experimental-theoretical examination of optical, electronic and morphological properties of novel 2D materials and their utilization in VOC gas sensor field, by means of several characterization techniques and density functional theory (DFT). Aside from the basic familiarization with the experimental and theoretical methodology in Chapter 2, examination of the functionalization of exfoliated MoS2 using DDT (1-Dodecanethiol) in Chapter 3, which eventually led to a research paper. The DDT treatment is incorporated into the NMP (N-methyl pyrrolidone) exfoliation procedure, resulting in successful functionalization as confirmed by optical, morphological, and theoretical analysis. Raman spectroscopy showed the formation of graphitic species on MoS2 sheets, with decreased sulfur-vacant sites as the DDT ratio increased. STEM and AFM data confirmed the presence of graphitic quantum dots (GQDs) on MoS2 nanosheets, while PL intensities demonstrated significant improvements in photoluminescent properties. This study enhances our understanding of surface and edge chemistry in exfoliated MoS2 and expands the possibilities for broader applications of MoS2 and GQD particles. Moreover, the attention was drawn to the investigation of the contrasting responses of graphene gas sensors fabricated using different synthesis methods, in the submitted paper explained in Chapter 4. Exfoliated graphene sensors decrease in current when exposed to methanol, while CVD graphene sensors increase in current. The differences in edge site population and electrical properties contribute to these responses. The study provided theoretical and experimental findings for an understanding of the reasons behind the inverse sensor responses of CVD and exfoliated graphene on an atomic scale.Master Thesis Graphene-Like Materials for Electronic Applications(01. Izmir Institute of Technology, 2020) Başkurt, Mehmet; Şahin, Hasan; Balcı, SinanTwo-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 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, HasanA 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 Monitoring the Diffusion and Degradation Characteristics of Crystals Via Raman Spectroscopy(Izmir Institute of Technology, 2018) Akbalı, Barış; Şahin, HasanLamellar structures, having strong in-plane and weak (van der Waals) out-ofplane bonding, exhibit extraordinary properties when thinned down to their monolayer limit. Following the isolation of single layer graphene in 2004, there has been a rapid increase in the number of studies focusing on other novel two dimensional (2D) materials such as hexagonal Boron Nitride (BN), transition metal dichalcogenides (TMDs), post transition metal chalcogenides (PTMCs), silicene and black-phosphorus. Doping of 2D and bulk crystals is a well-known strategy that may lead to novel functionalities and significantly alters materials’ electronic, optical, and magnetic properties. In this regard, understanding of diffusion characteristic of dopant in a crystal via computational simulation is vital to enlighten physical insights of the experiment. In addition, investigation of degradation mechanisms of crystals at atomic-level is also still open question. In this sense, the density functional theory (DFT) is one of the most powerful and commonly used methods for such theoretical investigations. Moreover, measuring vibrational spectra of a material via Raman spectroscopy is powerful method to understand atomic vibrations that give information about physical properties of a material. In this regards, we investigate diffusion characteristics and degradation mechanism of several crystal (such as, perovskites and MoS2) by means of first-principles calculations based on density functional theory (DFT). In addition, Raman measurements are also carried out to investigate vibrational properties of the crystals. It is shown that few-layer MoS2 can be used for selective nitrogenation of graphene. In addition, red shift in photoluminescence peak of water interacted CsPbBr3 nanowires arise from detachment of surface ligand from surface of nanowire by presense of water molecules. Lastly, time-dependent photoluminescence measurement of Mn-doped CsPbCl3 shows that change in emission color under UV illumination is due to segregation of Mn atoms towards crystal surface. This thesis provides some important results for deeper understanding of degradation and diffusion mechanisms of dopants in 2D materials and perovskites.