Weak Response of Metallic Single-Walled Carbon Nanotubes to C₆₀ Encapsulation Studied by Resonance Raman Spectroscopy

Metallic single-walled carbon nanotubes (SWCNTs) have been regarded as unique quasi-1D metallic systems. Their basic properties significantly differ from those of their semiconducting counterparts even though their chemical compositions and sizes are nearly identical to each other. In this study, we investigate the effects of C₆₀ fullerene encapsulation on the phonon and electronic properties of metallic SWCNTs by resonance Raman spectroscopy. The changes in the radial breathing mode frequencies and the optical transition energies after C₆₀ insertions show characteristic tube diameter dependences, as in the case of the corresponding semiconducting SWCNTs. Although the observed behaviors can be attributed to the intermolecular interaction between SWCNTs and the encapsulated C₆₀, similar to the corresponding semiconducting SWCNTs, the strength of the interaction is measurably weaker than that of semiconducting SWCNTs. The present findings provide important insight into the essential differences in the basic nature of metallic and semiconducting SWCNTs

Length-Dependent Plasmon Resonance in Single-Walled Carbon Nanotubes

The optical response of single-walled carbon nanotubes (SWCNTs) to far-infrared (FIR) radiation was systematically studied using various SWCNTs with different tube-length distributions. The observed peak position in the FIR spectra linearly scaled with the inverse of tube length irrespective of diameter, which is consistent with the dispersion relation predicted by the one-dimensional plasmon resonance model. The effects of chemical doping on the FIR spectra of the separated metallic and semiconducting SWCNTs clearly indicate that the motion of plasmons in the electronic band structures is primarily responsible for the optical response in these spectral regions. The observed absorption peaks are naturally sensitive to the presence of defects on the tube wall and correlated with the electric resistance, suggesting that the plasmons resonate with the current path length of the SWCNTs

Spectroscopic Characterization of Nanohybrids Consisting of Single-walled Carbon Nanotubes and Fullerodendron

<div><p>Hydrogen gas, which can be used in fuel cells to generate electricity, is considered the ultimate clean energy source. Recently, it was reported that a photo-induced electron transfer system consisting of single-walled carbon nanotubes (SWCNTs) and fullerodendrons shows photo-catalytic activity with a very high quantum yield for splitting water under visible light irradiation. However, the mechanism of high efficiency hydrogen generation is not yet clearly understood. We report here the spectroscopic characterizations of the SWCNT-fullerodendron composites. The results indicate two important fundamental properties of the composite system. First, fullerodendrons preferentially interact with the semiconducting SWCNTs instead of with their metallic counterparts. Second, the photo-induced electron transfer process from the C₆₀ moiety of fullerodendrons to SWCNTs occurs more efficiently with an increasing tube diameter.</p> </div