Static Dielectric Properties of Carbon Nanotubes from First Principles (original) (raw)
Related papers
Electronic structure and dielectric behavior of finite-length single-walled carbon nanotubes
4th IEEE Conference on Nanotechnology, 2004.
The electronic structure and dielectric screening of finite-length armchair carbon nanotubes are studied within a tight-binding model, which well captures the oscillation pattern of the band gap as the tube length increases. We find that: (1) the parallel screening constant || grows almost linearly with the length and shows little dependence on the band gap; (2) the perpendicular screening is strongly related to the band gap and ⊥ converges to its bulk value when the length exceeds tens of radius. Our method is employed to study the depolarization effect of a short (6,6) nanotube in a wet environment, when water is inside the tube. This situation is of interest for biomimetic uses of carbon nanotubes.
Influence of external electric fields on electronic response and bandstructure of carbon nanotubes
We performed tight-binding calculation of the electronic properties of carbon nanotubes in a perpendicular electric field. Within the linear response limit, the dielectric function of a doped carbon nanotube is found to depend not only on its symmetry, but also on the Fermi level position and tube radius. Upon increasing the field, the mixing of neighboring subbands results in metal-semiconductor transitions in both quasi-metallic and semiconducting nanotubes. The characteristic field strength of the transitions is calculated as a function of the tube radius. An optimal radius range to be used for band gap engineering is estimated for both types.
Effect of electric field on the electronic structures of carbon nanotubes
Applied Physics Letters, 2001
We have investigated the electronic structures of a capped single-walled carbon nanotube under the applied electric field using density functional calculations. The capped tube withstands field strengths up to 2 V/Å. When the electric field is applied along the tube axis, charges are transferred from the occupied levels localized at the top pentagon of the cap, and not from the highest occupied level localized at the side pentagon, to the unoccupied levels. We find that the charge densities at the top of the armchair cap show two-or five-lobed patterns depending on the field strength, whereas those of the zigzag cap show a three-lobed pattern. The interpretation for the images of the field emission microscope is also discussed.
First-Principles Study of Dielectric Constant and Polarizability in Two Carbon Nanotubes
Asian Journal of Science and Applied Technology ISSN: 2249-0698 Vol. 7, No.1, 2018, pp.8-10, 2018
First-principles calculations have been carried out on two Carbon Nanotubes having 54 and 72 carbon atoms. The Electronic density of state reveals that the materials show metallic nature. Dielectric constant has been computed in case of Carbon Nanotubes C54 and C72. The value of dielectric constant in Carbon Nanotube C54 comes out to be 7.06, 6.28 and 14.53 along X, Y and Z axes respectively and its average value comes out to be 9.29. Value of dielectric constant in Carbon Nanotube C72 comes out to be 167, 168 and 737 along X, Y and Z axes respectively and its average value comes out to be 357. Polarizability of Carbon Nanotube C54 has been estimated and it comes out to be 116(Å) 3 , 111(Å) 3 and 142(Å) 3 along X, Y and Z axis respectively. Polarizability in case of Carbon Nanotube C72 comes out to be 171(Å) 3 , 171(Å) 3 and 173(Å) 3 along X, Y and Z axes respectively.
2013
Optical dispersion spectra at energies up to 30 eV play a vital role in understanding the chirality-dependent van der Waals London dispersion interactions of single wall carbon nanotubes (SWCNTs). We use one-electron theory based calculations to obtain the band structures and the frequency dependent dielectric response function from 0-30 eV for 64 SWCNTs differing in radius, electronic structure classification, and geometry. The resulting optical dispersion properties can be categorized over three distinct energy intervals (M, π, and σ, respectively representing 0-0.1, 0.1-5, and 5-30 eV regions) and over radii above or below the zone-folding limit of 0.7 nm. While π peaks vary systematically with radius for a given electronic structure type, σ peaks are independent of tube radius above the zone folding limit and depend entirely on SWCNT geometry. We also observe the so-called metal paradox, where a SWCNT has a metallic band structure and continuous density of states through the Fermi level but still behaves optically like a material with a large optical band gap between M and π regions. This paradox appears to be unique to armchair and large diameter zigzag nanotubes. Based on these calculated one-electron dielectric response functions we compute and review Van der Waals -London dispersion spectra, full spectral Hamaker coefficients, and van der Waals -London dispersion interaction energies for all calculated frequency dependent dielectric response functions. Our results are categorized using a new optical dielectric function classification scheme that groups the nanotubes according to observable trends and notable features (e.g. the metal paradox ) in the 0-30 eV part of the optical dispersion spectra. While the trends in these spectra begin to break down at the zone folding diameter limit, the trends in the related van der Waals -London dispersion spectra tend to remain stable all the way down to the smallest single wall carbon nanotubes in a given class.
Physical Review B, 2002
To investigate the dielectric response of isolated single-walled carbon nanotubes, ͑SWCNTs͒, spatially resolved electron energy-loss spectroscopy measurements have been carried out using a scanning transmission electron microscope in a near-field geometry. Spectra have been compared with those acquired on multiwalled carbon nanotubes ͑MWCNTs͒ made of different numbers of layers, and with simulations performed within the framework of the continuum dielectric theory, taking into account the local anisotropic character of these nanostructures and adapted to the cylindrical geometry. Experimental data show a dispersion of mode energies as a function of the ratio of the internal and external diameters, as predicted by the continuum dielectric model. For thin MWCNTs, two polarization modes have been identified at 15 and 19 eV, indexed as tangential and radial surface-plasmon modes, respectively, resulting from the coupling of the two surface modes on the internal and external surfaces of the nanotubes. We finally show that the dielectric response of a SWCNT, displaying a single energy mode at 15 eV, can be understood in the dielectric model as the thin layer limit of surface-plasmon excitation of MWCNTs.
Nano Letters, 2007
We report on a carbon nanotube network which is composed of aligned metallic and randomly oriented semiconducting single-walled carbon nanotubes. The material is formed by using a novel radio frequency dielectrophoresis setup, which generates very large dielectrophoretic force fields and allows dielectrophoretic assembling of nanotube films up to 100 nm thickness. Polarization dependent absorption measurements provide experimental evidence for the electronic type specific alignment behavior. We explain the experimental data with an advanced model for nanotube dielectrophoresis, which explicitly takes into account both the longitudinal and transversal polarizability. On the basis of this model, we calculate the dielectrophoretic force fields and show that semiconducting nanotubes deposit under very large fields due to their transversal polarizability even for high field frequencies.
Optoelectronic Properties of Single-Wall Carbon Nanotubes
Advanced Materials, 2012
diffraction is a powerful technique for the determination of atomic structure of individual nano-objects, as was demonstrated in Iijima's original work on multiwall [ 187 ] and singlewall [ 1 ] carbon nanotubes. However, it is not suited for studying a large number of carbon nanotubes. Therefore, optical spectroscopy has emerged in the last decade as the most convenient means for determining the chirality indices (n , m) of SWCNTs in macroscopic ensembles of SWCNTs. There is now a wellestablished correlation between optical transition energies, diameters, and (n , m) indices, as shown in Figure 2 a. [ 188 ] RRS spectroscopy has served as the most commonly used tool for (n , m) determination for both metallic and semiconducting SWCNTs for many years. [ 189 ] For semiconducting, or ν = ± 1, SWCNTs, PLE spectroscopy [ 24-35 ] can provide accurate information on the E 11 and E 22 energies from the emission and excitation photon energies, respectively, as shown in Figure 2 b. One can also combine PLE and RRS spectroscopies to determine E 33 and E 44 in semiconducting nanotubes. [ 190 ] Furthermore, as detailed in Section 3, coherent phonon spectroscopy has several advantages for simultaneously determining (n , m) indices and phonon frequencies for both semiconducting and metallic SWCNTs (see Figure 2 c). Finally, Section 4 presents how aligned SWCNT fi lms can be used to develop optoelectronic devices, ranging from state-of-the-art terahertz polarizers to large-area, broadband photodetectors. 2. Enrichment and Spectroscopy of Armchair Carbon Nanotubes Because of their excellent electrical properties, metallic SWCNTs are considered to be promising candidates for a variety of future electronic applications such as nanocircuit interconnects and power transmission cables. In particular, (n , n)-chirality, or 'armchair,' metallic nanotubes are theoretically predicted to be truly gapless and intrinsically insensitive to disorder, [ 191-192 ] consistent with experimentally observed ballistic conduction behavior at the single-tube level. Unfortunately, progress towards creating such ballistic-conducting armchair devices in bulk quantities has been slowed by the inherent problem of nanotube synthesis, whereby both semiconducting and metallic nanotubes are produced. Sébastien Nanot received his Ph.D. from Université de Toulouse (France) in 2009 under supervision by Profs. Bertrand Raquet and Jean-Marc Broto. His thesis focused on individual carbon nanotube properties under a very high magnetic fi eld. He moved to Rice University where he is appointed as a postdoctoral researcher in Prof. Junichiro Kono's group. His current research focuses on optoelectronic properties of carbon nanotubes ensembles.