Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Nanotribological Properties of Graphene Grown on Silicon Carbide Semiconductor(Izmir Institute of Technology, 2018) Keskin, Yasemin; Çelebi, Cem; Ünverdi, ÖzhanIn this thesis, nanotribological properties of single and multilayer graphene grown on two sides of the Silicon Carbide (SiC) semiconductors were investigated. For this purpose, epitaxial growth technique was used to obtain single-layer graphene on both C-face and Si-face. This thesis consists of two purposes: One of them is to investigate the nanotribological properties of the single and multilayer graphene grown on C-face of SiC and the other one is to compare nanotribological properties of the single layer graphene on two sides of SiC. Graphene, a two-dimensional semi-metal material, was grown epitaxially on the SiC surface under ultra-high vacuum conditions. In epitaxial method, direct current heating is applied to the SiC substrate to vaporize Si atoms from the surface. As the Si atoms evaporate, the remaining C atoms form a graphene layers on top. When single layer graphene is formed on the Si-face, multilayer graphene is formed on the C-face at the same parameters. For this reason, two different samples of graphene were needed in order to compare the tribological properties of the single layer graphene grown on both Si-face and C-face for the secondary objective. A capping method was used to control the rate of Si atoms evaporating from the SiC surface. By this way, single layer graphene on the C-face was obtained too. Number of layers were determined by Raman Spectroscopy. Nanotribological characterizations were done with Atomic Force Microscopy. The experimental results showed that single layer graphene on the Si-face has higher friction coefficient compared to single layer graphene on the C-face. It has been found that the single layer graphene (0.02) formed on the C-surface has a lower coefficient of friction than the multilayer graphene (0.82). It is expected that with the support of the theoretical studies on this results will increase the interest in this study by means of these results are new and original for the literature.Master Thesis Field Emission Electron Source Based on Silicon Carbide Nanopillars(Izmir Institute of Technology, 2017) Yeşilpınar, Damla; Çelebi, Cem; Demir, Mustafa MuammerIn this thesis work, I studied the fabrication and the field emission characteristics of SiC nanopillar based electron field emitters. The first objective of this thesis was to fabricate a large area nanopillar array on bulk 6H-SiC substrate. Accordingly, a nanosphere assisted technique was developed to create a conventional Cr/Ni hard mask to acquire desired etch mask pattern on the C-terminated face of 6H-SiC. The nanopillars were then fabricated by ICP-RIE. Two sets of nanopillars with different aspect ratios and geometries were fabricated for two different ICP-RIE durations. 1 min long etch resulted in nanopillar arrays with blunt tip apex and an aspect ratio of 3.4, where 2 min long etch produced nanopillar arrays with an aspect ratio of 4.9 and a sharp tip apex with an estimated radius of curvature of about 18 nm. As the second objective; the electron field emission characteristics of the produced nanopillars with two different aspect ratios and geometries were investigated and the obtained results were compared with each other. We found that the nanopillars with sharp tip apex produced field emission currents up to 240 μA/cm2 under 17.4 V/μm applied electric field, as the nanopillars with blunt tip apex produced an emission current of 70 μA/cm2. The threshold electric fields were found to be 9.1 V/μm and 7.2 V/μm for the nanopillars with blunt and sharp tip apex, respectively. Time dependent stability measurements yielded stable electron emission without any abrupt change in the respective current levels of both samples.