Loss spectra of graphite-related systems: A multiwall carbon nanotube, a single-wall carbon nanotube bundle, and graphite layers

Abstract

The -electron excitations are studied for a multiwall carbon nanotube, a single-wall carbon nanotube bundle with finite nanotubes, and graphite layers. The loss spectra of the nanotube systems exhibit several plasmon peaks. The most prominent one is the plasmon, and the others are the interband plasmons. The latter are absent in graphite layers. The plasmon depends on the number of carbon nanotubes or graphite layers ͑N͒, the transferred momentum ͑q͒, and the transferred angular momentum ͑L͒. The intertube or interlayer Coulomb interactions clearly enhance -plasmon frequency and oscillator strength as N increases. A multiwall carbon nanotube can exhibit L-decoupled plasmons. For the Lϭ0 plasmon, the multiwall nanotube behaves like graphite layers, but not like a single-wall carbon nanotube bundle. The radius dependence is negligible for a multiwall nanotube, while it is strong for a single-wall nanotube bundle. Furthermore, the former exhibits stronger collective excitations, higher -plasmon frequency, and relatively rapid increase of plasmon frequency with q. The calculated results are compared with experimental measurements.

Visible and near ultraviolet photocurrent generation in carbon nanotubes

“…In particular, DWCNTs have been found to generate photocurrent in the infrared and visible regions and the peaks in the observed photocurrent spectra have been related to the electronic transitions between van Hove singularities in their electron density of states [3]. This is consistent with energy loss spectra calculations performed for single and multiwall carbon nanotubes, predicting the presence of interband electronic transitions due to the reduced dimensionality of these systems [1]. In the present paper, we show that (i) MWCNTs are able to generate a photocurrent in the visible and near ultraviolet energy regions (ii) features are present in the photocurrent spectra at excitation photon energy in the visible range; (iii) peaks at energies between 2.2 and 4 eV are detected in the electron energy loss spectra, in addition to the typical graphite p plasmon .…”

“…These systems are closely related to graphite layers and are generally considered to exhibit similar electronic properties. On the other hand, the MWCNTs electronic density of states is difficult to model, due to the high number of shells and their mutual interactions and, therefore, only few theoretical predictions of their electronic properties are available [1]. Theoretical and experimental efforts have been dedicated to double wall carbon nanotubes (DWCNTs), being the simplest form of multiwall carbon nanotube [2][3][4].…”

UV–vis absorption spectroscopy of carbon nanotubes: Relationship between the π-electron plasmon and nanotube diameter

“…Most early studies using wider nanotubes observed no dependence of the p plasmon resonance on diameter, although it has been shown that it is strongly polarisation dependent in aligned nanotubes [18] and both bulk and surface plasmon effects have been invoked [19,20]. Electron energy loss measurements, which tend to the absorption results at a momentum transfer of zero, report a range of values [21][22][23] with the specific value recorded depending on both the bundling state and nanotube alignment, although the typical SWNT diameter used in these studies is 1.4-2.0 nm. As the energies of the p plasmon absorbance recorded in this study are consistent with those previously reported for SWNT (and MWNT) and we observe a clear shift in the energy of the p plasmon absorbance across samples, direct correlation with a number of the structural characteristics of the bulk nanotube samples was possible.…”

“…Despite the fact that these spectroscopic signatures can, in theory, be conveniently probed using conventional analytical techniques, specifically the use of UV-vis spectroscopy to assess the p plasmon absorbance, few examples exist in the scientific literature and to date and the best of our knowledge there are no systematic studies which look to correlate the morphological and structural characteristics of the bulk nanotube sample with the position and intensity of the p plasmon absorbance. Furthermore, advanced techniques, such as electron energy loss spectroscopy (EELS) and a variety of theoretical approaches have yielded somewhat ambiguous and contradictory results in recent times [13][14][15][16][17][18][19][20][21][22][23]. In this communication, we report for the first time a comprehensive study of the p plasmon absorbance of a series of SWNT using ultraviolet-visible (UV-vis) spectroscopy.…”

Linear Plasmon Dispersion in Single-Wall Carbon Nanotubes and the Collective Excitation Spectrum of Graphene

“…Angle resolved electron energy loss spectroscopy (EELS) assesses the detailed plasmon dispersion [7,8], but it is so far missing for freestanding isolated sp 2 carbon systems. Models based on the homogeneous electron gas [9], or the tight-binding scheme [10,11] have been used to describe these excitations. The former are however bound to metallic systems.…”