Browsing by Subject "CVD"
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Item Open Access CVD synthesis and characterization of thin Mo2C crystals(Wiley, 2020) Türker, F.; Caylan, Ö. R.; Mehmood, Naveed; Kasırga, Talip S.; Şevik, C.; Cambaz-Büke, G.In this study, we present an investigation on the growth of thin Mo2C crystals via chemical vapor deposition using CH4. Optical microscopy (OM), scanning electron microscopy (SEM), atomic force microscopy(AFM), and Raman spectroscopy studies show that the morphology and the thickness of Mo2C crystals are strongly affected by the impurities in the system, the thickness of the copper substrate, and the graphene presence on Cu surface prior to Mo2C formation. Our studies show that during the CVD process, orthorhombic Mo2C crystals grow along the [100] direction on two different regions: directly on Cu surface or on graphene covered regions. Mo2C crystals that form on graphene are found to be thinner and less defective compared to the ones formed on the Cu surface. This is attributed to graphene acting as an additional diffusion barrier for Mo atoms diffusing through the copper. In addition to the graphene beneath the Mo2C crystal, Raman studies indicate that graphene may grow also on top of the Mo2C crystal, forming a graphene/Mo2C/graphene sandwich structure which may offer interesting properties for electronic applications.Item Open Access Graphene based high frequency electronics(Bilkent University, 2010) Pinçe, ErçağRecent advances in chemical vapor deposition of graphene on large area substrates stimulate a significant research effort in order to search for new applications of graphene in the field of unusual electronics such as macroelectronics. The primary aim of this work is to use single layer of graphene for applications of high frequency electronics. This thesis consists of both theoretical and experimental studies of graphene transistors for the use of radio frequency electronics. We have grown graphene layer using chemical vapor deposition technique on large area copper substrates. The grown graphene layers are then transferred onto dielectric substrates for the fabrication of graphene transistors. The theoretical part of the thesis is focused on the understanding the performance limits of the graphene transistor for high frequency operation. We investigate the intrinsic high frequency performance of graphene field effect transistors using a self consistent transport model. The self-consistent transport model is based on a nonuniversal diffusive transport that is governed by the charged impurity scattering. The output and transfer characteristics of graphene field effect transistors are characterized as a function of impurity concentration and dielectric constant of the gate insulator. These experimental and theoretical studies shape the basis of our research on the graphene based radio frequency electronics.Item Open Access Probing interfacial processes on carbon nanotubes and graphene surfaces(Bilkent University, 2012) Kakenov, NurbekThe surface of low-dimensional carbon (carbon nanotubes and graphene) has unique electronic properties due to the delocalized p-orbitals. Very high carrier mobility with nanoscale dimension make carbon nanotubes and graphene promising candidates for high performance electronics. Besides electronic properties, the delocalized orbitals have a strong tendency to adsorb aromatic molecules via p-electronic interactions. The strong non-covalent interactions between the graphitic surface and organic molecules provide a unique template for supramolecular chemistry and sensing applications. A comprehensive understanding of these forces at atomic and molecular level still remains a challenge. In this thesis, we have used carbon nanotube networks and graphene as model systems to understand molecular interactions on carbon surface. We have developed processes to integrate these model materials with sensitive and surface specific sensors, such as surface plasmon sensor and quartz crystal microbalance. In the first part of the thesis, we integrated surface plasmon resonance (SPR) sensors with networks of single-walled carbon nanotubes to study interactions between SWNT and organic molecules. In the second part, we probe interfacial processes on graphene surface by mass detection. We anticipate that the developed methods could provide a sensitive means of detecting fundamental interaction on carbon surfaces.