Absorption Spectra Of Carbon Nanotubes Research Articles

Excitons states and linear absorption spectra of carbon nanotubes with Stone–Wales defects

The exciton states in the single-walled carbon nanotubes (SWNTs) with Stone–Wales (SW) defects are theoretically studied in the tight-binding model. It is found that for the semiconducting zigzag tubes (10, 0) with different concentration of SW defect, the exciton energies move to low energy region with increasing the concentration of SW defect, and the symmetry broken by the SW defects leads to splitting of the degenerate exciton energy levels, which can be seen clearly from the linear absorption spectra of defected SWNTs. As detected from the linear absorption spectra, we can give some information on the concentration of the SW defect existing in the SWNTs.

Absorption spectrum of carbon nanotubes in the space

Graphene C$_{24}$ was recently identified in interstellar space through its characteristic infrared vibrational spectra. As graphene can bend to form carbon nanotubes (CNTs), one of the focuses of ultraviolet and infrared space telescopes is to search for interstellar CNTs. Here, we calculate the absorption spectrum of (5, 0) CNT, the smallest CNT, using the discrete dipole approximation. (5, 0) CNT exhibits four spectral features, peaking at $\sim$0.3, $\sim$0.5, $\sim$0.9, and $\sim$2.9 $\mu$m, with the peak wavelengths shifting toward the red region with the increasing tube length. When the tube length is longer than 23 carbon atoms, the $\sim$2.9 $\mu$m peak becomes quite prominent. Moreover, the absorption spectrum converges if the number of dipoles is at least ten times that of the C–C bonds.

Twisted angle effects in the absorption spectra of carbon nanotube

The spectral characteristics of carbon nanotubes is essential for the development of optoelectronic components and sensors with application in many fields. The linear polarizability absorption spectra of the carbon nanotube with a twisted angle have been calculated by using the tight-binding model and sum-over-state method. First, a structural model of carbon nanotubes based on PPP(Pariser-Parr_Pople) was established, then a certain carbon atom was moved to a position where the carbon nanotubes are angled, and the torsional carbon nanotube structure model was calculated based on the change in bond length. Finally, the absorption spectrum at different twisted angles based on SOS(Sum-over-State) was calculated, and then the detailed analysis was made. It is found that the twisted angle has real impact on the absorption spectra of different types carbon nanotubes. The torsional angle leads to changes in the position and number of absorption peaks of the carbon nanotubes. Its influence on absorption spectra of different types of carbon nanotubes is different, but mainly concentrated in the low frequency region. Exactly, altering the twisted angle has an important effect on the absorption spectra of the carbon nanotube. This work offers a guidance of fabricating carbon nanotubes in the applications of photonic device in many fields.

Absorption Spectrum of Carbon Nanotubes

Carbon nanotubes are very typical nanomaterials, because the electron π of carbon nanotubes is restricted by the quantum size, the energy bands of the electron π are discontiguous and the characteristic of its energy level is divisive. The electron π can absorb the photon and makes transition from low energy level to high energy level, so it has the characteristic of wave-absorption . Based on the theory of quantum mechanics and the atomic structure of carbon nanotubes, the electronic energy bands and absorption spectrum of carbon nanotubes are analyzed in this paper, the results show that carbon nanotubes of different size correspond with absorption spectrum of different wave bands, and the computational results are afforded for the bases of designing wave-absorption materials.

Energy spectrum and optical absorption spectra of carbon nanotubes with chiralities of (10, 10), (11, 9), and (12, 8)

The energy spectra of single-wall carbon nanotubes (CNTs) with chiralities of (10, 10), (11, 9), and (12, 8) are calculated in the static fluctuation approximation for the Hubbard model. The choice of these systems for investigation was dictated by the fact that these systems are the most typical of heterogeneous samples obtained by synthesis. It is shown that in the chosen model and approximation, the type of conduction is independent of chirality, which contradicts the generally accepted opinion concerning the critical dependence of the CNT conduction current on the chirality indices. The optical absorption spectra of the CNTs under investigation are calculated using the resultant energy spectra. The shape of the optical absorption spectrum averaged over the known weight composition is in good agreement with experimental data. The results of investigation suggest that the rule according to which CNTs exhibit metal-type conductivity when the difference in the chirality indices is a multiple of three; otherwise, they have the semiconductor-type conductivity, is in all probability not general, but has applicability limits that can be established by rigorous calculations based on the Hubbard model.

The effect of light polarization on the interband transition spectra of zigzag carbon nanotubes and its diameter dependence

Although the optical absorption spectra of carbon nanotubes with perpendicularly polarized light are known to be suppressed due to the depolarization effect, peaks with significant magnitudes have been reported in photoluminescence absorption spectra of single-walled nanotubes under perpendicular polarization. We study the effect of light polarization on the interband optical transition spectra of nanotubes, independently from the depolarization effect. We employ the density functional theory to calculate the absorption spectra of periodic zigzag carbon nanotubes for parallel and perpendicular polarization of light in a wide, infrared-visible-ultraviolet range (0–11eV). We have chosen (4,0), (8,0), and (16,0) nanotubes with diameters of ~0.34, ~0.63, and ~1.27nm, respectively, to also investigate the dependence of the polarization effect on nanotube diameter. Although the overall spectrum for perpendicular polarization is sparse compared to the one for parallel polarization, the transition probability can be quite significant at certain photon energies for perpendicular polarization. For an (8,0) nanotube, for example, we observe sharp peaks at 1.2eV, 1.8eV and 10.6eV. As the nanotube diameter decreases, parallel polarization seems to become progressively more favorable for absorption than perpendicular polarization in the infrared/visible range. Surprisingly, in the ultraviolet region, this trend is reversed; for nanotubes with small diameter, we notice a higher probability of absorption for ultraviolet light with perpendicular polarization compared to the one with parallel polarization. This can be important in optoelectronic applications of carbon nanotubes for ultraviolet absorption and emission.

Selection rules and linear absorption spectra of carbon nanotubes in axial magnetic fields

We derive a transparent and easy-to-use analytic expression for the selection rules and the optical dipole matrix elements for carbon nanotubes of arbitrary chirality in the presence of axial magnetic fields using a single-orbital \ensuremath{\pi}-electron tight-binding model. From this, we calculate the linear absorption spectrum for arbitrary polarization directions of the incident light, providing insight into all optically allowed transition. We show that the transverse absorption peaks can be selectively excited with circularly polarized light and spectrally resolved in an axial magnetic field.

Defect electron states in carbon nanotubes and graphite from the NEXAFS spectroscopy data

Experimental results of studying the electronic structure of single-walled and multi-walled carbon nanotubes as well as graphite by X-ray absorption spectroscopy (or NEXAFS spectroscopy) are presented. The C1s absorption spectra are measured with high energy resolution using the equipment of the Russian-German beamline of the BESSY electron storage ring. Features found in absorption spectra of carbon nanotubes and graphite for the first time are interpreted in the case of carbon nanotubes as the contribution of electron states appearing due to the imperfection of their structure both under the nonequilibrium synthesis conditions and during the subsequent producing manipulations.

Temperature dependence of exciton-phonon-induced sidebands in arbitrary carbon nanotubes

We present a microscopic approach based on the many-body density matrix formalism for the study of exciton–phonon-induced features in absorption spectra of carbon nanotubes with an arbitrary chiral angle and diameter. The introduction of excitonic wave functions already containing the influence of the Coulomb interaction allows us to focus on the contribution of phonons. We observe the formation of pronounced sidebands on both sides of the zero-phonon line. We study the behaviour of exemplary nanotubes belonging to the two semiconducting and one metallic family with respect to the spectral weight transfer from the zero-phonon line to the exciton–phonon sidebands at different temperatures.

Effects of oxygen adsorption on the electronic structure and optical properties of single-wall carbon nanotubes

The binding energy,energy band structure and optical properties of the oxygen physical adsorption on semiconducting single_wall carbon nanotube are studied by the density functional theory. The most stable adsorption site is the one in which the oxygen molecule lies above the center of the carbon ring. It is showed th at the oxygen physical adsorption strongly affects the transport properties and the optical absorption spectra of carbon nanotubes. And the phenomenon of oxygen photoinduced desorption has been explained theoretically.

Magneto-optical spectra of carbon nanotubes: effect of Aharonov–Bohm flux on depolarization effect

Optical absorption spectra of carbon nanotubes in a magnetic field perpendicular to the tube axis, are calculated for parallel polarization. A depolarization field is induced by Aharonov–Bohm flux, which reduces the lowest peak dramatically.