Indexed on: 01 May '04Published on: 01 May '04Published in: Applied Physics A
Single-walled carbon nanotubes (SWNTs) of 0.4 nm in diameter are produced inside channels of microporous zeolite single crystals. Three possible structures: (5,0), (4,2), and (3,3) contribute to three bands at 1.37, 2.1, and 3.1 eV in optical absorption spectra. The direct correspondence between chiralities and absorption bands is identified by density functional calculations. The resonant Raman spectrum shows the features that can be assigned to van Have singularities in calculated phonon density of states. In the low-frequency region, two peaks at 510 and 550 cm-1 are attributed to the radial breathing modes (RBMs) of the (5,0) and (4,2) tubes. After removing the zeolite framework, the RBM frequencies downshift by ∼10 cm-1. The charge-transfer behavior in lithium-doped 0.4-nm SWNTs is investigated. The Raman peak at 1558 cm-1 couples with the electronic continuum, and shows a Breit–Wigner–Fano line shape.