The origin of polarized blackbody radiation from resistively heated multiwalled carbon nanotubes

We observed very pronounced polarization of light emitted by highly aligned free-standing multiwall carbon nanotube (MWNT) sheet in axial direction which is turned to the perpendicular polarization when a number of layers are increased. The radiation spectrum of resistively heated MWNT sheet closely follows to the Plank's blackbody radiation distribution. The obtained polarization features can be described by a classical dielectric cylindrical shell model, taking into consideration the contribution of delocalized π-electrons (π surface plasmons). In absorption (emission) the optical transverse polarizability, which is much smaller than longitudinal one, is substantially suppressed by depolarization effect due to screening by induced charges. This phenomenon suggests very simple and precise method to estimate the alignment of nanotubes in bundles or large assemblies.     

On the electronic band structure of zigzag-type single-walled carbon nanotubes

The electronic band structure of a zigzag-type carbon nanotube has been computed by using the tight-binding approximation method in the framework of SSH Model Hamiltonian modified by the inclusion of two Lagrange multipliers instead of one. This modification yielded an electronic band structure consistent with the experimental reports that an infinite (3,0) zigzag-type single-walled carbon nanotubes displays a metallic behaviour.     

Optical response of small-diameter semiconducting carbon nanotubes under exciton-surface-plasmon coupling

We analyze the optical response of small-diameter (?1 nm) semiconducting carbon nanotubes under the exciton-surface-plasmon coupling. Calculated optical absorption lineshapes exhibit the significant line (Rabi) splitting ∼0.1-0.3 eV as the exciton energy is tuned to the nearest interband surface plasmon resonance of the nanotube so that the mixed strongly coupled surface plasmon-exciton excitations are formed. We discuss possible ways to bring the exciton in resonance with the surface plasmon. The exciton-plasmon Rabi splitting effect we predict here for an individual carbon nanotube is close in its magnitude to that previously reported for hybrid plasmonic nanostructures artificially fabricated of organic semiconductors deposited on metallic films. We believe this effect may be used for the development of carbon nanotube based tunable optoelectronic device applications in areas such as nanophotonics and cavity quantum electrodynamics.     

Review on the symmetry-related properties of carbon nanotubes

In this work we review the basic properties of carbon nanotubes from the standpoint of group theory. The zone folding scheme is reviewed in the light of the helical symmetry of the nanotube. The group theory for chiral and achiral nanotubes is reviewed, and the representations of the factor group of the wavevector k are obtained. The similarities and differences between the formalism of the group of the wavevector and that of line groups are addressed with respect to the irreducible representations and quantum numbers associated with linear and angular momenta. Finally, we extend the results of group theory to illuminate the electronic and vibrational properties of carbon nanotubes. Selection rules for the optical absorption and double resonance Raman scattering are discussed for the case where the electron–electron interaction is negligible (metallic nanotubes) and for the case where exciton binding energies are strong and cannot be neglected.     

Interwall conductance in double-walled armchair carbon nanotubes

The dependence of the interwall conductance on distance between walls and relative positions of walls are calculated at the low voltage by Bardeen method for (n,n)@(2n,2n) double-walled carbon nanotubes (DWCNTs) with n=5,6,…,10. The calculations show that interwall conductance does not depend on temperature (for T?500 K) and current-voltage characteristic is linear. The conductance decreases by 6 orders of magnitude when the interwall distance is doubled. Thus, depending on the interwall distance, DWCNTs can be used as temperature stable nanoresistors or nanocapacitors.     

First-principles study of the electronic and optical properties of rutile TiO2

The electronic, structural properties and optical properties of the rutile TiO₂ have been reported using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We employed the generalized gradient approximation (GGA), which is based on exchange-correlation energy optimization to calculate the total energy. Also we have used the Engel-Vosko GGA formalism, which optimizes the corresponding potential for band structure calculations. Our results including lattice parameter, bulk modulus, density of states, the reflectivity spectra, the refractive index and band gap are compared with the experimental data. We present calculations of the frequency-dependent complex dielectric function ε(ω) and its zero-frequency limit ε₁(0).     

Two modes of electroluminescence from single‐walled carbon nanotubes

The electroluminescence from single‐walled carbon nanotube field effect transistors is spectrally resolved, and shows two distinct modes of light emission. The vast majority of nanotubes have spectrally broad emission consistent with the spectrum of blackbody radiation. Much more rarely, superposed on the broad emission is a single narrow (<50 meV) peak which is consistent with expectation for electron–hole recombination. The narrow emission is strong even at lower biases and in general has greater peak intensity than the broadband emission. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Plasmon hybridization in metallic nanotubes

We study theoretical formalism of the plasmon hybridization in a metallic nanotube and find an explicit form of the dispersion relation for surface plasmons, in terms of interaction between the bare plasmon modes of the individual surfaces of the nanotubes. In the special case when the longitudinal wave vector is zero (q=0), the plasmon hybridization of a nanotube has a behavior similar to the spherical nanoshell.     

First-principles band structures of armchair nanotubes

Received: 10 February 1998     

Effects of electronic state modulation on the high-frequency response characteristics of GaAs quantum wells

The effect of electronic-state modulation on the high frequency response of GaAs quantum well with thin inserted barrier layer is studied. The carrier scattering by polar optic phonons, acoustic deformation potential and background ionized impurities are incorporated in the present calculations considering the carrier distribution to be heated drifted Fermi-Dirac distribution. Modified phonon spectra and modulated electron wave function give different values of form factor compared to bulk mode phonon. Mobility is found to be enhanced on insertion of thin layer inside the quantum well. The ac mobility and the phase lag increases with the increase in both the channel width and the 2D carrier concentration. Cutoff frequency, where ac mobility drops down to 0.707 of its low frequency value, is observed to be enhanced reflecting better high frequency response.     

Hopping conduction in disordered carbon nanotubes

We report electrical transport measurements on individual disordered multiwalled carbon nanotubes, grown catalytically in a nanoporous anodic aluminum oxide template. In both as-grown and annealed types of nanotubes, the low-field conductance shows an exp[−(T₀/T)^1/2] dependence on temperature T, suggesting that hopping conduction is the dominant transport mechanism, albeit with different disorder-related coefficients T₀. The electric field dependence of low-temperature conductance behaves as exp[−(ξ₀/ξ)^1/2] at high electric field ξ at sufficiently low T. Finally, both annealed and unannealed nanotubes exhibit weak positive magnetoresistance at . Comparison with theory indicates that our data are best explained by Coulomb-gap variable-range hopping conduction and permits the extraction of disorder-dependent localization length and dielectric constant.     

First-principles calculations on the origins of the gap bowing in InAs1-xPx alloys

We perform self-consistent ab-initio calculations to study the structural, electronic and thermodynamic properties of InAs_1-xP_x alloy. The full potential-linearized augmented plane wave (FP-LAPW) method was employed within density functional theory (DFT). The ground-state properties are determined for the bulk materials (InAs and InP) as well as for the different concentration of their alloys. Deviations of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. The gap bowing for the alloy of interest was found to be mainly caused by the charge-exchange contributions. In addition, the thermodynamic stability of InAs_1-xP_x alloy was investigated by calculating the excess enthalpy of mixing ΔH_m and the calculated phase diagram showed a broad miscibility gap with a high critical temperature.     

Plasmon hybridization in metallic nanotubes with a nonconcentric core

We develop a theory of plasmon excitations in a metallic nanotube with a nonconcentric core using the plasmon hybridization method. We apply the two-center cylindrical coordinate system for mathematical convenience and find an explicit form of the dispersion relation for surface plasmons, in terms of interaction between the bare plasmon modes of the individual surfaces of the nanotubes. We present numerical result displaying the effect of the offset distant d of the inner core from the nanotube center, when there is no angular momentum transfer, i.e., m=0. For large offsets, the plasmon shifts is strong, but weak for small offset.     

Proton channeling through long chiral carbon nanotubes: The rainbow route to equilibration

In this work we investigate the rainbows appearing in channeling of 1 GeV protons through the long (11,9) single-wall carbon nanotubes. The nanotube length is varied from 10 to 500 μm. The angular distributions of channeled protons are computed using the numerical solution of the proton equations of motion in the transverse plane and the Monte Carlo method. The rainbows are identified as the rings in the angular distributions, which correspond to the extrema of the proton deflection functions. Each rainbow is characterized by a sharp decrease of the proton yield on its large angle side. As the nanotube length increases, the number of rainbows increases and the average distance between them decreases in an easily predictable way. When the average distance between the rainbows becomes smaller than the resolution of the angular distribution, one cannot distinguish between the adjacent rainbows, and the angular distribution becomes equilibrated. We call this route to equilibration the rainbow route to equilibration. This work is a demonstration of how a simple one-dimensional bound dynamic system can exhibit a complex collective behavior.     

The dielectric constant of barium mono-chalcogenides and their improved band gap results

We have applied Engel-Vosko exchange energy within density functional theory, to calculate the electronic structure and the optical properties of BaX (X = Te, Se, and S) compounds via full potential linearized augmented plane wave method. We have found that this improves the band gap results comparing to our previous work in which we had made use of Perdew et al. exchange energy functional. We have also calculated the dielectric constant of these compounds, using both Perdew et al. and Engel-Vosko schemes. It is shown that Engel-Vosko exchange energy functional leads to a better result. We have also reported the effect of spin-orbit coupling on the results.     

Free standing double walled boron nanotubes

Based on density functional calculations we propose stable structures of free standing double walled boron nanotubes in the form of two single walled boron nanotubes (SWBNTs) inside one another. Puckering of the boron sheets allows the inner atoms of the outer wall and outer atoms of the inner wall to be matched giving sp-type hybrid σ bonding between the walls. The structural stability, in the case of double walled tubes, increases as the bond interaction between the walls strengthens. All the optimized structures reported in this study are electronically conducting in good agreement with the previously calculated metallic behavior of the experimentally observed SWBNTs.     

Adsorption and electrochemistry of hemoglobin on Chi-carbon nanotubes composite film

This study describes the noncovalently functionalization of carbon nanotubes (CNTs) with natural biopolymer chitosan (Chi) as substrate for hemoglobin (Hb) immobilization. The noncovalently Chi-functionalized CNTs possessed an improved solubility in aqueous solution and was beneficial to form three-dimensional configuration of the CNTs film electrode. The adsorbed Hb in Chi-CNTs interface showed a pair of quasi-reversible redox peak with a formal potential of −0.34 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffer solution and possessed good bioelectrochemical catalytic activities toward the reductions of H₂O₂.     

Effect of doping on electronic properties of double-walled carbon and boron nitride hetero-nanotubes

The effect of boron nitride (BN) doping on electronic properties of armchair double-walled carbon and hetero-nanotubes is studied using ab initio molecular dynamics method. The armchair double-walled hetero-nanotubes are predicted to be semiconductor and their electronic structures depend strongly on the electronic properties of the single-walled carbon nanotube. It is found that electronic structures of BN-doped double-walled hetero-nanotubes are intermediate between those of double-walled boron nitride nanotubes and double-walled carbon and boron nitride hetero-nanotubes. Increasing the amount of doping leads to a stronger intertube interaction and also increases the energy gap.