GCRIS

Now showing 1 - 3 of 3

Two Dimensional Material Based Field Effect Transistor for Biosensing Applications
(01. Izmir Institute of Technology, 2023) İnanç, Dilce; Yıldız, Ümit Hakan; Çelebi, Cem
This thesis presents research on the use of two-dimensional material graphene as an area-effective transistor and its application in biological fields. The formation of wrinkled and flat structures on the surface of a single-layer graphene area-effective transistor, epitaxially grown for determining the bio-membrane dynamics of graphene, was examined using two different methods of deposition (thermal evaporation and pulsed electron accumulation) of a silicon dioxide (SiO2) layer. The investigation aimed to evaluate the pH and lipid bilayer formation performance of both wrinkled and flat GFETs. Increased sensitivity was determined through electrical measurements, as the oxide layer becomes thinner due to the existence of wrinkles, thus providing electrostatic coating on graphene. A sensor platform of chemiresistor type was developed for the differential determination of volatile organic compounds (VOCs) by synthesizing single-layer, bilayer, and multilayer graphene, enabling the analysis of ethanol (EtOH) and methanol (MetOH). Sensors produced using three different graphene morphologies demonstrated differential MeOH-EtOH responses attributed to the differential intercalation phenomenon in multilayer graphene morphologies when compared to ethanol. For the detection of VOCs such as acetone, ethanol, and hexane in human breath, a polymer nanofiber/multi-walled carbon nanotube or poly (3,4-ethylenedioxythiophene)/gold (Au) and iron oxide (Fe) hybrid bioelectronic interface was developed. Sensitivity studies were conducted by applying pure VOCs at different concentrations to the sensor platforms, and the behavior of the sensor platforms against interfering elements was evaluated by recharacterizing them under CO2 and humidity conditions. Considering the responses of MWCNT-PLLCL-Fe-based sensors to acetone, ethanol, and hexane, the tendency of water molecules to adhere to the Fe surface was shown to decrease water condensation on the conductive layer compared to other sensor configurations, indicating that the humidity effect was minimized in MWCNT-PLLCL-Fe-based sensors.
Optical Properties of Ultra-Thin Materials
(Izmir Institute of Technology, 2017) Bacaksız, Cihan; Senger, Ramazan Tuğrul; Şahin, Hasan
Many years of research effort, after the synthesis of graphene, have revealed that atomically thin two-dimensional materials have mechanical, electronic, and optical properties which are different from their bulk counterparts. Thus, the interest in twodimensional materials is growing which is also fueled by fast advances in synthesis and measurement techniques. In this regard, the theoretical and computational simulations provide physical insight to the experiments in this new and demanded field; a tool for characterizing these materials; and also a reliable prediction approach to possible stable structures. The density functional theory (DFT) is one of the most powerful and commonly used methods for such theoretical investigations. The DFT-based computational determination of optical properties, as compared to other usual DFT-based calculations, is in its early stage due to high computational resource requirements and lack of established documentation. Therefore, the present thesis aims at giving the methodology and computing the optical properties of ultra-thin materials by using DFT and beyond-DFT approaches. More precisely, the thesis provides an overview of light matter interaction; basics of DFT, GW approximation for many-body effects, Bethe-Salpeter equation for excitonic effects; and several applications of these on atomically-thin systems.
Electronic, Magnetic, and Mechanical Properties of Novel Two Dimensional Monolayer Materials
(Izmir Institute of Technology, 2017) Yağmurcukardeş, Mehmet; Senger, Ramazan Tuğrul; Şahin, Hasan
Layered materials exhibit different properties when they are thinned down to a few monolayers. Following the successful isolation of 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), and in-plane anisotropic monolayers (Redichalcogenides and blackphosphorus). In addition to their electronic, optical, and magnetic properties, mechanical properties of 2D materials are of fundamental importance. Measurements of elastic constants of 2D materials are still challenging. Therefore, theoretical investigation of the mechanical properties is particularly important. Moreover, investigation of Raman spectra of these materials requires a through understanding of their vibrational properties. In these regards, we investigate the electronic, magnetic, and mechanical properties of some novel monolayer 2D materials (such as, auxetic pentagonal monolayers, flexible monolayers of holey graphene crystals, ultra-flexible monolayers of PTMCs, and in-plane anisotropic monolayers of ReS2 and blackphosphorus) by means of first-principles calculations based on density functional theory (DFT). In addition, tuning electronic properties of a van der Waals heterobilayer structure composed of monolayers of Mg(OH)2 and WS2 upon an external out-of-plane electric field is studied. The effect of biaxial strain on the vibrational properties of novel 2D materials is also studied through their off-resonant Raman activities. Our findings will be useful to clarify several issues related to the experiments of novel 2D materials.

Phd Degree / Doktora

Browse

Filters

Settings

Sort By

Results per page

Search Results