Master Degree / Yüksek Lisans Tezleri

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

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Subject: search.filters.subject.Chemical vapor deposition

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  • Master Thesis
    Synthesis and Nitrogen Doping of Graphene by Chemical Vapor Deposition
    (Izmir Institute of Technology, 2017) Yanılmaz, Alper; Çelebi, Cem; Adem, Umut; Çelebi, Cem; Adem, Umut; 03.09. Department of Materials Science and Engineering; 04.05. Department of Pyhsics; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of Technology
    Controllable carrier transport due to charged impurities in the graphene lattice is still lacking. Doping of graphene by foreign atoms leads to modify its band structure and electro chemical properties. Among numerous potential dopants, nitrogen (N2) is considered to be an excellent candidate to form strong valence bonds with carbon atoms, which would provide n or p-doping according to bonding character of charged-impurity atom. Exposure of graphene lattice to nitrogen gas leads to a change in the carrier concentration and opens a bandgap due to symmetry breaking. Furthermore, this seems to be an effective way to customize the properties of graphene and exploit its potential for various applications. This thesis focuses on the growth of graphene by low pressure chemical vapor deposition (LPCVD) and doping it with N2 by using N2 plasma treatment. Here, copper foil was used as the catalytic substrate to grow large area graphene at LPCVD system. The grown graphene was transferred onto SiO2, Au (111) and Sapphire substrates. The effect of different plasma time and power on doping process was investigated while keeping the N2 flow rates constant by using N2 plasma. The nitrogen doped graphene (N-graphene) was characterized via Raman Spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy/spectroscopy (STM/STS), Kelvin probe force microscopy (KPFM). Raman mapping of N-graphene was also conducted to show the homogeneity of N2 incorporation into graphitic lattice. STM results were theoretically modelled by using density functional theory (DFT). Our results provide the opportunity to produce N-graphene with homogenous and effective doping which would be valuable in electronic and optoelectronic applications.
  • Master Thesis
    Influence of Ni Thin Flim Structural Properties Over Graphene Growth by Cvd
    (Izmir Institute of Technology, 2013) Özçeri, Elif; Selamet, Yusuf; Selamet, Yusuf; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    This thesis work focused on the effect of polycrystalline Nickel (Ni) TM thin film structure on the growth graphene by chemical vapor deposition (CVD). TM films were deposited by magnetron sputtering technique on Si/SiO2 substrates. To grow 1-2 layer graphene on Ni thin film catalyst by methane decomposition thermal CVD method was carried out using various growth parameters. To reduce the TM film surface roughness and grow larger size graphene layers on Ni film, Si/SiO2 substrates were coated by a thin Al2O3 buffer layers and Cr adhesive layers by magnetron sputtering. Ni film crystal structure and surface roughness, which affected the number of graphene layers, were examined by X-ray Diffraction (XRD) and Atomic Force Microscopy (AFM) techniques, respectively. The thickness and columnar structure of the films were measured from Surface Profiler and Scanning Electron Microscopy (SEM) images. Ni films were annealed at 800 oC, 900 oC and 950 oC in order to improve their crystal quality and to evaluate the effect of the crystallinity on graphene growth at atmospheric pressure. Samples were studied using XRD and AFM also to assess their crystal quality after the annealing process. It was observed that the calculated grain sizes depended on the film thickness and the annealing temperature. Surface roughness of the films was increased by increasing film thickness. A sole thin Al2O3 buffer layer reduced the surface roughness significantly. However, sole Cr adhesive layer or Cr/Al2O3 buffer layers did not reduce the surface roughness, but increased the crystallinity of Ni films in (111) direction. Argon, Hydrogen or a mixture of these two gases was added to methane during graphene growth at ambient pressure by CVD. The Raman spectroscopy was utilized in order to determine the number of the layers and quality of graphene growth over the Ni catalyst film.
  • Master Thesis
    The Effects of Oxidizers on the Diameters of the Carbon Naotubes Grown by Chemical Vapor Deposition Method
    (Izmir Institute of Technology, 2012) Bülbül, Gülay; Selamet, Yusuf; Selamet, Yusuf; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    This thesis was focused on growing high quality and small-diameter carbon (C) nanotube (NT) on Fe/Al2O3/SiO2/Si thin film catalyst by ethylene decomposition thermal chemical vapor deposition (CVD) method in the presence of a weak oxidizer (CO2). Moreover, the importance and functional properties of the oxidizer in pretreatment and CNT growth were determined. At first, it was worked in different growth conditions to examine the effects of CO2 in CNT growth. The main parameters were pretreatment time, CO2 gas flow rates during pretreatment and growth, growth temperature. Pretreatment and growth times were kept at 15 min. each and CO2 introduced 5 and 10 min. during pretreatment stage prior to the CNT growth with the flow rates 8:2, 10:2, 10:8 and 10:10 sccm, respectively. Additionally, three different growth temperatures; 750 oC, 760 oC and 770 oC were studied. Secondly, pretreatment time was kept at 15 min. The effects of CO2, which was sent in the system at 8:2, 10:2, 10:8 and 10:10 sccm ratios, on density and height of the catalyst particles were investigated. At last, all catalyst particles and CNTs obtained from the experiments were analyzed by several characterization techniques such as AFM, EDX, SEM, STEM and Raman Spectroscopy, respectively. The optimal values of amount and introduction time of CO2, the ratio of CO2 in growth to that in pretreatment were identified. Moreover, the relation between currently obtained catalyst particles and previously being grown CNTs on them were determined. It was observed that using the appropriate amount of CO2 in pretreatment and growth process positively affected the catalyst sizes and CNT diameter distributions.