Structural ( n, m) determination of isolated single-wall carbon nanotubes by resonant Raman scattering.

TLDR: It is shown that the Raman scattering technique can give complete structural information for one-dimensional systems, such as carbon nanotubes, by measuring one radial breathing mode frequency omega(RBM) and using the theory of resonant transitions.

Abstract: We show that the Raman scattering technique can give complete structural information for one-dimensional systems, such as carbon nanotubes. Resonant confocal micro-Raman spectroscopy of an (n,m) individual single-wall nanotube makes it possible to assign its chirality uniquely by measuring one radial breathing mode frequency omega(RBM) and using the theory of resonant transitions. A unique chirality assignment can be made for both metallic and semiconducting nanotubes of diameter d(t), using the parameters gamma(0) = 2.9 eV and omega(RBM) = 248/d(t). For example, the strong RBM intensity observed at 156 cm(-1) for 785 nm laser excitation is assigned to the (13,10) metallic chiral nanotube on a Si/SiO2 surface.

Figures

FIG. 3. (a) Measured frequency vs intensity for the RBM peaks observed at 42 different spots on the sample (Fig. 1). (b) Calculated energy separation Eii as a function of 1#dt , g0 ! 2.9 eV, and vRBM ! 248#dt . Circles are for metallic SWNTs (EMii ), and crosses for semiconducting SWNTs (E S ii).

FIG. 2. Raman spectra from three different spots on the Si substrate, showing only one resonant nanotube and one RBM frequency for each of 3 spots. The RBM frequencies (widths) and !n, m" assignment for each resonant SWNT are displayed. The 303 cm21 feature comes from the Si substrate. Inset (a) shows Raman spectra from one spot on the sample, including 303, 521, and 963 cm21 Raman features from the Si substrate. Inset (b) shows a zoom of the corresponding G-band region.

TABLE II. Possible chiralities predicted for semiconducting nanotubes and their vRBM (calculated and observed) in the resonant window 1.48 , ES22 , 1.68 eV.

FIG. 1. AFM images of the sample. The small particles are iron catalysts. The inset shows the diameter distribution of the sample taken from 40 observed SWNTs.

TABLE I. Possible chiralities predicted for metallic nanotubes and their calculated vRBM in the resonant window 1.48 , EM11 , 1.68 eV. We also display the observed vRBM, with the number of times each appears between parentheses.