Diameter selective reaction processes of single-wall carbon nanotubes

A method is presented which allows the study of diameter selective reactions in single-wall carbon nanotubes with an unprecedented accuracy. It is based on the transformation of fullerene peapods into double-wall carbon nanotubes and the study of the resulting diameter distribution of the inner nanotubes with Raman spectroscopy. This yields a spectral resolution increase of about 40 for the modes of different tubes. The method is demonstrated for the diameter selective healing of nanotube defects and yield from ${\mathrm{C}}_{70}$ peapod samples. The growth of very small diameter inner tubes from ${\mathrm{C}}_{70}$ peapods is demonstrated, which challenges the models of inner nanotube formation. An anomalous absence of middiameter inner tubes is explained by the suppressed amount of ${\mathrm{C}}_{70}$ peapods in the transition region between standing and lying ${\mathrm{C}}_{70}$ configurations.

Figure 1

As measured Raman spectra of the inner nanotube RBMs for four 60-DWCNT samples (lower curves in each quarter) at $\lambda =647\mathrm{nm}$ laser excitation. The upper spectra are smart scaled from the lower left spectrum. The Gaussian diameter distribution is shown for the DWCNT-L sample.

Figure 2

Raman spectra of untreated tubes (a), tubes heated at $800°\mathrm{C}$ prior to filling (b), and ratio of the inner tube signal intensity for the heat treated $\left({\mathrm{I}}_{\text{treated}}\right)$ and the untreated material $\left({\mathrm{I}}_0\right)$ (c). The lowest scale shows the diameters of the corresponding outer tubes.

Figure 3

Comparison of the Raman spectra of 60-DWCNT-R (lower spectra) and 70-DWCNT-R (upper spectra) for $\lambda =515$, 647, 755, and $1064\mathrm{nm}$, respectively. Solid arrows indicate the (7,5) and (5,3) nanotubes in the $755\mathrm{nm}$ spectra and the (4,4) nanotube on the 1064 spectra. Dashed arrows mark the vicinity of the $362\pm 3{\mathrm{cm}}^{-1}$ spectral range.

Figure 4

Normalized intensity ratios of the Raman RBM modes of inner tubes in 60-, and 70-DWCNT-R materials at all laser lines studied. The data are sliding averaged as explained in the text. The dashed curve is a guide to the eye.