Master Degree / Yüksek Lisans Tezleri

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

Browse

Filters

2020 - 20245

Settings

Access type: Open accessSubject: search.filters.subject.Two-dimensional materials

Search Results

Now showing 1 - 5 of 5
  • Master Thesis
    Machine-learning-assisted de novo design of molybdenum disulfide binding peptides
    (01. Izmir Institute of Technology, 2024) Öğüt, Alp Deniz; Yücesoy, Deniz Tanıl; Apaydın, Mehmet Serkan
    Kısa amino asit zincirleri, peptitler, biyolojik süreçler ve yüksek teknoloji uygulamaları için vazgeçilmez moleküllerdir. Geniş kullanım alanları arasında, moleküler tanıma özelliği ile bio-nano arayüzler oluşturmak ilgi toplayan bir araştırma konusu olmuştur. Yapılan çalışmalar sonucunda yönlendirilmiş evrim metodolojileri oluşturulmuş ve çeşitli hedeflere -enzim, antijen veya inorganik yapılar- bağlanan fonksiyonel peptit tanısı mümkün hale gelmiştir fakat bu geleneksel yaklaşım ölçeklenebilirlik ve sekans uzayındaki ilişkilerin anlaşılması konusunda zayıflıklar taşımaktadır. Bu zafiyetler, yüksek çıktılı sekanslama ve hesaplama verimlerinin artması ile beraber derin yönlendirilmiş evrim gibi daha güçlü teknolojilerinin geliştirilmesini motive etmiştir. Bu yöntemle üretilen büyük veri setleri, sekans-fonksiyon ilişkilerinin makine öğrenmesi ile modellenebilmesinin önünü açmıştır. Bu tezin amacı bu veri setlerine uygun bir makine öğrenmesi akışı oluşturmaktır. Bu düzlemde Random Forest algoritması ve derin nöral ağlar kullanılmış, eğitilen modellerin bağlanma puanı öngörüleri beraber kullanıldığında mutlak hata sırasıyla, 0.0304, Pearson korelasyon ölçütü 0.904 olarak elde edilmiştir. Bu modelleri kullanarak rastgele arama ve tekrarlayan optimizasyonlar ile güçlü bağlanan örnek bir peptit tasarlanmıştır. Bulgular alan bilgisinin makine öğrenme modeli eğitimdeki yerini vurgulamış, kullanılan örnek ağırlıklarının ve semantik amino asit vektörlerinin başarıya önemli katkıları gözlemlenmiştir. Bu çalışma çeşitli fonksiyonlara sahip peptit tasarlayabilen bir platform oluşturabilmek için temel noktaları göz önüne serer.
  • Master Thesis
    Electronic Properties of Correlated Impurities in Two Dimensional Materials
    (01. Izmir Institute of Technology, 2023) Dolu, Volkan; Çakır, Özgür
    This Master's thesis investigates the effects of single and dual impurity potentials on the electronic properties of both pristine and gapped graphene, being examples of two-dimensional materials. The behavior of 2D materials at the atomic levels, particularly graphene, has been of interest due to their particular electronic properties, such as high electron mobility at certain conditions. The presence of impurities may significantly influence these properties, providing a modifiable platform for rearranging electronic characteristics for diverse applications. Our research focuses on how the impurity states that emerge, especially around energies at low DOS, affect the electronic structure and the interaction between the impurities. We study these effects in the presence of both single and dual impurity potentials of varied strength using computational models based on tight-binding approach. We begin by looking at how the single impurity potentials affect the electronic properties of pristine graphene and gapped graphene. We analyze the change in DOS and energy of the system, along with the identification of the impurity states, utilizing participation ratio for localization. Then, we extend our study to dual impurity potentials and their impacts to provide a knowledge of multi-impurity scenarios. We explore the interaction of the impurities mediated by the Fermi sea. In particular, we studied the hybridization of impurity states and corresponding impurity energies. Next, we determine the force arising between impurities for various Fermi energies, impurity-impurity distances and impurity potential strengths for graphene and gapped graphene.
  • Master Thesis
    First-Principles Investigation of Novel Single-Layers and Heterostructures of Group Iii-Iv Elements
    (01. Izmir Institute of Technology, 2022) Yayak, Yankı Öncü; Yıldız, Ümit Hakan
    Since the discovery of graphene, two-dimensional materials have been the focus of interest in various branches in scientific community. Wide range of ultra-thin materials have been investigated both theoretically and experimentally such as metal chalcogenides, Xenes and h-BN. In addition to this, two-dimensional (2D) van der Waals heterojunctions have become one of the central research topics due to their wide range of possibilities. Since 2D van der Waals heterostructures are combinations of two or more ultra-thin materials with different properties, creating a heterostructure with desired optical, electrical and/or mechanical property is theoretically probable. Motivated by these, this thesis focus on the investigation of structural, vibrational and electronic properties of 2D materials and their heterostructures by means of density functional theory-based first-principle calculations. In chapter 3, single-layer Ge3N4 is shown to be both electronically and dynamically stable. Also, simulated Raman spectrum of single-layer Ge3N4 have characteristic vibrational properties. Another property of single-layer Ge3N4 is that it is a indirect band gap semiconductor and this property is uneffected by external strain. And lastly, the value of band gap varies with the applied external strain. In chapter 4, a dynamically stable single layer structure of AlAs is proposed and four possible stackings of AlAs/InSe heterobilayer were investigated. Electronic band dispersions revealed that all four stackings are direct band gap semiconductors and have type-II alignment. Moreover, simumlated raman spectra revelaed that identification of the 1T and 2H phase can be done with Raman spectroscopy. The band gap can be tuned based on the direction and magnitude of the electric field. Direct to indirect band gap transition as well as heterojunction type changes from type II to type I occurs under negative electric field.
  • Master Thesis
    Identification of Single-Layer Crystalline Structures Through Their Electronic and Optical Properties
    (01. Izmir Institute of Technology, 2021) Sözen, Yiğit; Şahin, Hasan; Balcı, Sinan
    A large number of two-dimensional (2D) van der Waals type materials have become a focus of interest in many scientific fields, ever since the thinnest carbon compound, graphene, takes to the stage with its exceptional electronic properties. The outstanding electronic behavior resulting from quantum size effects requires an investigation of the electronic and optical features of materials at the atomic scale. The understanding of such properties of matter within the framework of the theoretical approaches is the first step to shed light on the discovery of electronic and optoelectronic devices including brand new features. This thesis discusses the identification of electronic and optical properties of several types of atomically thin crystals, consisting of 2D and lead-free perovskite structures, by means of density functional theory (DFT). In the first study, primarily, the strong interaction mechanism between Ge atom and single-layer GaAs was studied starting from single atom adsorption to detached germanene layer formation. Following that dynamically stable metallic structures of Janus and alloy type GaGeAs crystals are discovered by performing one-sided and alternated decoration of GaAs single-layer with Ge atoms, respectively. %The Raman spectroscopy is found to be applicable for phase detection as the theoretically calculated Raman spectra of each polytype exhibit distinctive signals. In the second study, bulk and dynamically stable ultra-thin structures of lead-free CsMnCl$_3$ are discussed. According to total energy and electronic band structure calculations, bulk, bilayer, and single-layer structures of CsMnCl$_3$ are robust antiferromagnetic insulators. In third and fourth chapters are devoted to the identification of different stacking types of GaP/GaSe heterobilayers, and two different hexagonal phases of single-layer Germanium Oxide by means of electronic and optical characterization tools, respectively. In these studies, for the purpose of providing an accurate solution for the prediction of absorption, reflectance, and transmission spectra of materials, excitonic effects are considered by employing Bethe-Salpeter formalism following the $G_0W_0$ approximation. Wide range of atomically thin crystal structures studied within the framework of this thesis are verified to be promising candidates for the development of future nano-sized electronic and optoelectronic device applications thanks to their attractive electronic and optical properties arising from strong quantum confinement effects.
  • 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.