Raman spectroscopy of single wall carbon nanotubes grown in zeolite crystals

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.