Browsing by Subject "carbon"
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Item Open Access Compound Hertzian chain model for copper-carbon nanocomposites' absorption spectrum(2011) Kokabi, A.; Hosseini, M.; Saeedi, S.; Moftakharzadeh, A.; Vesaghi, M.A.; Fardmanesh, M.The infrared range optical absorption mechanism of carbon-copper composite thin layer coated on the diamond-like carbon buffer layer has been investigated. By consideration of weak interactions between copper nanoparticles in their network, optical absorption is modelled using their coherent dipole behaviour induced by the electromagnetic radiation. The copper nanoparticles in the bulk of carbon are assumed as a chain of plasmonic dipoles, which have coupling resonance. Considering nearest neighbour interactions for this metallic nanoparticles, surface plasmon resonance frequency (ω 0) and coupled plasmon resonance frequency (ω 1) have been computed. The damping rate against wavelength is derived, which leads to the derivation of the optical absorption spectrum in terms of ω 0 and ω 1. The dependency of the absorption peaks to the particle size and the particle mean spacing is also investigated. The absorption spectrum is measured for different Cu-C thin films with various Cu particle size and spacing. The experimental results of absorption are compared with the obtained analytical ones. © 2011 The Institution of Engineering and Technology.Item Open Access Metal coverage on single-wall carbon nanotubes : metal nanoring and nanotube formation(Bilkent University, 2002) Bağcı, V. M. KemalThe carbon nanotubes are welcomed as the basis element for electronic and opto-electronic devices of nanometers size, the size of a few atoms. The question of crucial importance in the physics of utilization of nanotubes as nanowires, transistors, couplers etc. is the metal-nanotube interactions. In this thesis, we considered the problem of metal coverage of nanotubes and single atom-metal interactions, using the first-principles computational techniques. We had found that Ti, Fe and Ni bind strongly to the nanotube while Al, Cu and Au has weak binding. We propose that d orbital electrons of transition metal elements play important role in the strong interactions. We also observed that strong metalmetal interaction prevents uniform coverage of nanotube, however a stable ring and tube of aluminum atoms with well defined patterns can also form around the semiconducting SWNT’s and lead to metallization. We have obtained a criteria for the uniform coverage of nanotubes by metal atoms.Item Open Access Six low-strain zinc-blende half metals: An ab initio investigation(2003) Pask J.E.; Yang L.H.; Fong, C.Y.; Pickett W.E.; Dag, S.A class of spintronic materials, the zinc-blende (ZB) half metals, has recently been synthesized in thin-film form. We apply all-electron and pseudopotential ab initio methods to investigate the electronic and structural properties of ZB Mn and Cr pnictides and carbides, and find six compounds to be half metallic at or near their respective equilibrium lattice constants, making them excellent candidates for growth at low strain. Based on these findings, we further propose substrates on which the growth may be accomplished with minimum strain. Our findings are supported by the recent successful synthesis of ZB CrAs on GaAs and ZB CrSb on GaSb, where our predicted equilibrium lattice constants are within 0.5% of the lattice constants of the substrates on which the growth was accomplished. We confirm previous theoretical results for ZB MnAs, but find ZB MnSb to be half metallic at its equilibrium lattice constant, whereas previous work has found it to be only nearly so. We report here two low-strain half metallic ZB compounds, CrP and MnC, and suggest appropriate substrates for each. Unlike the other five compounds, we predict ZB MnC to become/remain half metallic with compression rather than expansion, and to exhibit metallicity in the minority-rather than majority-spin channel. These fundamentally different properties of MnC can be connected to substantially greater p-d hybridization and d-d overlap, and correspondingly larger bonding-antibonding splitting and smaller exchange splitting. We examine the relative stability of each of the six ZB compounds against NiAs and MnP structures, and find stabilities for the compounds not yet grown comparable to those already grown.