共查询到20条相似文献,搜索用时 62 毫秒
1.
We study theoretically the interactions of excitonic states with surface electromagnetic modes of small-diameter (≲1 nm) semiconducting
single-walled carbon nanotubes. We show that these interactions can result in strong exciton-surface-plasmon coupling. The
exciton absorption lineshape exhibits the 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 expect this
effect to open up paths to new tunable optoelectronic device applications of semiconducting carbon nanotubes. 相似文献
2.
Kikuo Harigaya 《Journal of Physics and Chemistry of Solids》2010,71(4):627-629
Exciton effects are studied in single-wall boron-nitride nanotubes. The Coulomb interaction dependence of the band gap, the optical gap, and the binding energy of excitons are discussed. The optical gap of the (5,0) nanotube is about 6 eV at the on-site interaction U=2t with the hopping integral t=1.1 eV. The binding energy of the exciton is 0.50 eV for these parameters. This energy agrees well with that of other theoretical investigations. We find that the energy gap and the binding energy are almost independent of the geometries of nanotubes. This novel property is in contrast with that of the carbon nanotubes, which show metallic and semiconducting properties depending on the chiralities. 相似文献
3.
We investigate singlet and triplet trion states in semiconducting carbon nanotubes using a one-dimensional model. It is concluded that singlet trion states in bind up to 13.6% stronger than exciton states, and that they lower the optical transition energy with up to 50% of the tight binding band gap energy. 相似文献
4.
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. 相似文献
5.
6.
Low-energy, dark excitonic states have recently been predicted to lie below the first bright (E11) exciton in semiconducting single-walled carbon nanotubes [Phys. Rev. Lett. 93, 157402 (2004)10.1103/PhysRevLett.93.157402]. Decay into such deep excitonic states is implicated as a mechanism which reduces photoluminescence quantum yields. In this study we report the first direct observation of deep excitons in SWNTs. Photoluminescence (PL) microscopy of suspended semiconducting single-walled carbon nanotubes (SWNTs) reveals weak emission satellites redshifted by approximately 38-45 and approximately 100-130 meV relative to the main E11 PL emission peaks. Similar satellites, redshifted by 95-145 meV depending on nanotube species, were also found in PL measurements of ensembles of SWNTs in water-surfactant dispersions. The relative intensities of these deep exciton emission features depend on the nanotube surroundings. 相似文献
7.
I. Cabria M. J. López J. A. Alonso 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,34(1-3):279-282
Density functional calculations of the physisorption of molecular
hydrogen and the dissociative atomic chemisorption on the external
surface of hexagonal and pentaheptite carbon nanotubes, have been
carried out. Physisorption binding energies are near 100 meV/molecule and are similar on metallic and semiconducting
nanotubes. Full coverage of the nanotube with one molecule per
graphitic hexagon decreases the binding energy per molecule.
Chemisorption binding energies per H atom are larger on
pentaheptites than on hexagonal carbon nanotubes. The molecular
physisorption and dissociative chemisorption states on
pentaheptites have very similar total energies (some chemisorbed
states are even slightly more stable than the physisorbed states),
while on hexagonal carbon nanotubes molecular physisorption is
more stable than dissociative chemisorption. However, a
substantial energy barrier has to be overcome to go from
physisorption to dissociative chemisorption in both types of
nanotubes. 相似文献
8.
Masami Kumagai Akihito Taguchi Toshihide Takagahara Takahisa Ohno Kousuke Yakubo 《Solid State Communications》2008,145(3):154-158
The exciton properties of thin nanotube structures are investigated theoretically. Anisotropic size dependencies have been found in the exciton binding energy, the kinetic energy for the relative motions of an electron and a hole, and the wavefunction. These anisotropies arise from the different boundary conditions in the tube-length and circumferential directions, namely, the topological features of nanotubes. We also found that it is possible to change the topology of exciton wavefunctions by varying the tube-length and the tube-radius. These findings suggest that the optical properties of nanotubes such as oscillator strength or nonlinear susceptibilities can be controlled by tuning the structural parameters, thus yielding a novel guiding principle for designing optical functional materials. 相似文献
9.
Masao Ichida Satoshi Sakoda Yumie Kiyohara Singo Saito Yasumitsu Miyata Hiromichi Kataura Ken-ichi Mizuno Hiroaki Ando 《Journal of luminescence》2008,128(5-6):952-955
We have studied 1D exciton relaxation dynamics in semiconducting single-walled carbon nanotubes (SWNTs) by femtosecond pump–probe experiments. The time evolution of change in transmittance ΔT/T induced by photo-excitation varies depending on the tube diameter. The decay time decreases with a decrease in the tube diameter. Pressure measurements have been conducted to explore the relaxation mechanism. The deformation potential estimated from the pressure dependence of photoluminescence spectra increases with decreasing tube diameter. This means that the exciton–phonon interaction becomes stronger in the smaller diameter tubes. The diameter dependences of decay time and deformation potential suggest that the exciton–phonon interaction plays an important role in exciton nonradiative relaxation process in semiconducting SWNTs. 相似文献
10.
We calculate the electron-phonon scattering and binding in semiconducting carbon nanotubes, within a tight-binding model. The mobility is derived using a multiband Boltzmann treatment. At high fields, the dominant scattering is interband scattering by LO phonons corresponding to the corners K of the graphene Brillouin zone. The drift velocity saturates at approximately half the graphene Fermi velocity. The calculated mobility as a function of temperature, electric field, and nanotube chirality are well reproduced by a simple interpolation formula. Polaronic binding give a band-gap renormalization of approximately 70 meV, an order of magnitude larger than expected. Coherence lengths can be quite long but are strongly energy dependent. 相似文献
11.
A. Kumar Singh V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,34(1-3):295-298
Using ab initio total energy calculations we demonstrate that the nanotubes of germanium with atomic structure based on an alternate prism and antiprism stacking of hexagonal rings, can be stabilized by metal encapsulation. The V or Nb doped infinite nanotube is metallic. However, Mo doping leads to the formation of a metal encapsulated direct band gap semiconducting nanotube of germanium. These nanotubes with metal dependent electronic properties could prove to be vital for the development of future nanotechnologies. 相似文献
12.
Y. Lü H. Liu B. Gu 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,74(4):499-506
In this paper we calculate the binding energy of an exciton using the tight-binding model and discuss the exciton distribution
in detail. We analytically explain the dependence of the
distribution direction of exciton on the chiral angle, and the distribution localization along the
tube axis and oscillating along the tube circumference. The size of exciton is estimated to be
slightly larger than the diameter of the nanotube and it shows two family patterns versus the
inverse of tube diameter as similar as in the exciton binding energy. 相似文献
13.
Linear and nonlinear excitonic absorption in semiconducting quantum wires crystallized in a dielectric matrix 总被引:1,自引:0,他引:1
V. S. Dneprovskii E. A. Zhukov E. A. Muljarov S. G. Tikhodeev 《Journal of Experimental and Theoretical Physics》1998,87(2):382-387
Spectra of linear and nonlinear absorption of GaAs and CdSe semiconducting quantum wires crystallized in a transparent dielectric
matrix (inside chrysotile-asbestos nanotubes) have been measured. Their features are interpreted in terms of excitonic transitions
and filling of the exciton phase space in the quantum wires. The theoretical model presented here has allowed us to calculate
the energies of excitonic transitions that are in qualitative agreement with experimental data. The calculated exciton binding
energies in quantum wires are a factor of several tens higher than in bulk semiconductors. The cause of this increase in the
exciton binding energy is not only the size quantization, but also the “dielectric enhancement,” i.e., stronger attraction
between electrons and holes owing to the large difference between permittivities of the semiconductor and dielectric matrix.
Zh. éksp. Teor. Fiz. 114, 700–710 (August 1998) 相似文献
14.
We present a theoretical analysis and first-principles calculation of the radiative lifetime of excitons in semiconducting carbon nanotubes. An intrinsic lifetime of the order of 10 ps is computed for the lowest optically active bright excitons. The intrinsic lifetime is, however, a rapid increasing function of the exciton momentum. Moreover, the electronic structure of the nanotubes dictates the existence of dark excitons near in energy to each bright exciton. Both effects strongly influence measured lifetime. Assuming a thermal occupation of bright and dark exciton bands, we find an effective lifetime of the order of 10 ns at room temperature, in good accord with recent experiments. 相似文献
15.
The effect of oxygenation on the electronic properties of semiconducting carbon nanotubes is studied from first principles. The O2 is found to bind to a single-walled nanotube with an adsorption energy of about 0.25 eV and to dope semiconducting nanotubes with hole carriers. Weak hybridization between carbon and oxygen is predicted for the valence-band edge states. The calculated density of states shows that weak coupling leads to conducting states near the band gap. The oxygen-induced gap closing for large-diameter semiconducting tubes is discussed as well. The influence of oxygen on the magnetic property is also addressed through a spin-polarized calculation and compared to experiment. 相似文献
16.
17.
We report benchmark calculations of electroabsorption in semiconducting single-walled carbon nanotubes that provide motivation to perform electroabsorption measurement on these systems. We show that electroabsorption can detect the continuum bands in different energy manifolds. Direct determination of the binding energies of excitons in higher manifolds thereby becomes possible. We also find that electroabsorption can provide evidence for Fano-type coupling between the second exciton and the lowest continuum band states. 相似文献
18.
Somayeh KhazaeiMohammad Khazaei Hosein CheraghchiVahid Daadmehr Yoshiyuki Kawazoe 《Physica B: Condensed Matter》2011,406(20):3885-3890
We have used a non-equilibrium surface Green's function matching formalism combined with a tight-binding Hamiltonian to consider the effect of different arrangements of pentagon rings on localization of density of states at the tip regions of semi-infinite capped carbon nanotubes. The transfer matrixes are obtained by an iterative procedure. The results demonstrate that the positions of the peaks near Fermi energy are remarkably affected by the relative locations of pentagons. It is observed that in thin nanotubes, carbon atoms belonging two neighboring pentagon rings have significant contribution in the localized states near fermi energy. From our calculations, it turns out that the metallic or semiconducting behavior of capped nanotubes in the tip regions depends on the metallic or semiconducting nature of their nanotube stems. 相似文献
19.
20.
We investigate the interaction of single-walled carbon nanotubes (SWCNTs) and methane molecule from the first principles. Adsorption energies are calculated, and methane affinities for the typical semiconducting and metallic nanotubes are compared. We also discuss role of the structural defects and nanotube curvature on the adsorption capability of the SWCNTs. We could observe larger adsorption energies for the metallic CNTs in comparison with the semiconducting CNTs. The obtained results for the zig zag nanotubes with various diameters reveal that the adsorption energy is higher for nanotubes with larger diameters. For defected tubes the adsorption energies are calculated for various configurations such as methane molecule approaching to the defect sites pentagon, hexagon, and heptagon in the tube surface. The results show that the introduce defects have an important contribution to the adsorption mechanism of the methane on SWNTs. 相似文献