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Ultra-small single-walled carbon nanotubes (SWNTs) were synthesized in the matrix of AlPO4-5 zeolite single crystals. Polarized and temperature-dependent micro-Raman spectra were investigated for this complex. Three dominant peaks were exhibited in the spectra, which could be related to the possible three structures of 0.4 nm SWNTs: the (5,0), (4,2), and (3,3). Due to the large curvature in such SWNTs, the σ and π unoccupied orbital have a mixing. This orbital rehybridization induced obvious softening in the radial breathing modes and smaller temperature-dependence of Raman active modes compared with tubes with larger diameters. [Copyright &y& Elsevier]

Raman spectra of single-wall carbon nanotubes produced in the channels of zeolite AFl single crystals have been analyzed in the light of the full symmetry group, the line group. The phonon dispersion curves of the tubes (5,0), (3,3), and (4,2) are calculated based on the lattice dynamical model and the phonon branches are assigned to their quantum numbers (irreducible representations). The structures of Raman spectra of different samples are reproduced well by the density of states of relevant Raman-active phonons. The result is useful to evaluate the contents of these tubes in real crystals where the contents are not well defined before. [ABSTRACT FROM AUTHOR]

We develop a lattice-dynamical model based on the screw symmetry of single-walled carbon nanotubes that allows for reducing the size of the dynamical matrix to six, for all tube chiralities. The model uses force constants derived from fitting to the phonon dispersion of 2D graphite. We present the calculation procedure in a clear and transparent way, making the model easier to follow. We calculate the phonon dispersions of a number of nanotubes of different chiralities. The splitting of two highest Raman active modes and the radial breathing mode frequency are studied by changing the tube diameter and chirality. [Copyright &y& Elsevier]

Experimental characterization and theoretical simulations both confirmed single-walled 0.4 nm carbon nanotubes (SWNTs) to be directly observable by high-resolution transmission electron microscopy (HRTEM), with amorphous carbon films as the supporting substrates. While the amorphous carbon film gave rise to a uniform contrast which can overwhelm that of the SWNTs lying flat on the substrate, inclining SWNTs with an angle greater than 30° to the supporting film were found to result in a notable contrast of paired dark fringes. This SWNT contrast could be further enhanced by changing the HRTEM defocus condition. [Copyright &y& Elsevier]

Single wall carbon nanotubes with diameter 0.4 nm grown in the channels of AlPO4-5 crystals were studied by Raman spectroscopy. Up to 21 different laser lines were used to characterize vibrational properties. Spectra depend strongly on the energy of the laser line used for excitation. It was found that only two types of nanotubes with different chiralities, (5,0) and (4,2), are responsible for the spectra observed. The frequencies of the radial breathing modes were reliable assigned. A strong response was also observed for frequencies ∼1250 cm−1. The positions of two such peaks assigned to the (5,0) do not depend on the laser energy whereas only one such a peak was observed for the (4,2) nanotube. Its frequency shifts with the laser energy like the D line of large diameter nanotubes, but the rate of the shift is only a half of the value known for the latter. We did not observe a radial breathing mode of the (3,3) tube even though a laser line close to the predicted resonance energy was used. On the other hand, we detected a possible presence of the (5,1) tube in the spectrum excited with the UV laser line. [Copyright &y& Elsevier]

Photo-induced electric current modulation is studied in AFI-SWCNs systems by visible and near infra-red laser light at room temperature. Remarkable polarization anisotropy in the modulation is observed. λ-dependence of the polarization anisotropy is analyzed by a simple model based on the optical anisotropy observed in absorption spectra. [Copyright &y& Elsevier]