Probing interfacial processes on carbon nanotubes and graphene surfaces

Ankara : The Department of Physics and the Graduate School of Engineering and Science of Bilkent University, 2012.Thesis (Master's) -- Bilkent University, 2012.Includes bibliographical references leaves 62-74.The 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.Kakenov, NurbekM.S

RETRATO EN EL PATIO [Material gráfico]

INCLUIDAS EN EL PEQUEÑO ÁLBUM FOTOGRÁFICO FAMILIAR DE LA COLECCIÓN LUIS SUÁREZ GALVÁNCopia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201

Grafen-tabanlı elektrik ayarlı terahertz optoelektroniği

Cataloged from PDF version of article.Thesis (Ph.D.): Bilkent University, Department of Physics, İhsan Doğramacı Bilkent University, 2016.Includes bibliographical references (leaves 111-120).Advances in terahertz (THz) research and technology, has bridged the gap between radio-frequency electronics and optics. More efficient control of THz waves would highly benefit noninvasive, high-resolution imaging and ultra-fast wireless communications. However, lack of active materials in THz, hinders the realization of these technologies. Graphene, 2d-crystal of carbon atoms, is a promising candidate for reconfigurable THz optoelectronics due to its unique electronic band structure which yields gate-tunable optical response. Here, we studied gate-tunable optical properties of graphene in THz frequencies. Using time-domain and continuous wave THz spectroscopy techniques, tunable Drude response of graphene is investigated at very high doping levels with Fermi energies up to 1 eV. Our results show that, transport scattering time decreases significantly with doping. Unlike conventional semiconductors, we observed nearly perfect electron-hole symmetry even at very high doping levels. In the second part, we implemented using these unique tunable properties for novel THz optoelectronic devices such as THz intensity modulators and THz spatial light modulators. These devices are based on various designs of mutually gated capacitive structures consisting of ionic liquid electrolyte sandwiched between graphene and metallic electrodes. Low insertion losses (50 %) over a broad spectrum (0.1-2 THz), and the simplicity of the device structure are the key attributes of graphene based THz devices. Furthermore, with the optimized device architectures, gate tunable coherent perfect absorption is observed in THz which yields modulation depth of nearly 100 %. The approaches developed in this work surpass the challenges of generating high carrier densities on graphene, and introduce low-loss devices with practical fabrication methods which we believe can lead to more responsive and sophisticated optoelectronic devices.by Nurbek Kakenov.Ph.D

Graphene-quantum dot hybrid optoelectronics at visible wavelengths

With exceptional electronic and gate-tunable optical properties, graphene provides new possibilities for active nanophotonic devices. Requirements of very large carrier density modulation, however, limit the operation of graphene based optical devices in the visible spectrum. Here, we report a unique approach that avoids these limitations and implements graphene into optoelectronic devices working in the visible spectrum. The approach relies on controlling nonradiative energy transfer between colloidal quantum-dots and graphene through gate-voltage induced tuning of the charge density of graphene. We demonstrate a new class of large area optoelectronic devices including fluorescent display and voltage-controlled color-variable devices working in the visible spectrum. We anticipate that the presented technique could provide new practical routes for active control of light-matter interaction at the nanometer scale, which could find new implications ranging from display technologies to quantum optics.European Research Council (ERC) ERC 682723 SmartGraphene; TUBITAK (113F278