RESUMO
Controlling the structure of single-wall carbon nanotubes during their synthesis by chemical vapor deposition remains a challenging issue. Here, using a specific synthesis protocol and ex situ transmission electron microscopy, we perform a statistical analysis of the structure of the tubes and of the catalyst particles from which they grow. We discriminate two nucleation modes, corresponding to different nanotube-particle junctions, that occur independently of the particle size. With the support of tight binding calculations, we show that a direct control of the nanotube diameter by the particle can only be achieved under growth conditions close to thermodynamic equilibrium.
RESUMO
We report on the first tunable resonant Raman scattering study performed on suspended isolated and coupled single-wall carbon nanotubes, unambiguously identified by electron diffraction. Besides the confirmation of the relation between the structural properties, the radial breathing frequency and the optical resonances for isolated metallic nanotubes, we evidence that interacting nanotubes experience drastic modifications of their resonance fingerprints. We first demonstrate a degeneracy lifting of an electronic level in a bundle of identical zigzag nanotubes. We then show the existence of a strong energy transfer mediated by a mechanical coupling between two nonidentical bundled nanotubes.
RESUMO
The radial breathing modes and tangential modes have been systematically measured on a large number of individual semiconducting single-wall carbon nanotubes (thin bundles) suspended between plots (free-standing single-wall carbon nanotubes). The strong intensity of the Raman spectra ensures the precision of the experimentally determined line shapes and frequencies of these modes. The diameter dependence of the frequencies of the tangential modes was measured. This dependence is discussed in relation with recent calculations. The present data confirm/contradict some previous interpretations.
