Raman scattering study of coalesced
single-walled carbon nanotubes
S.L. Fang
Rao
Nikolaev
R.E. Smalley
(
Kentucky,
<*p(0,21.6,0,9.5,0,0,g,"U.S.
English")$f"Helvetica-Condensed">High-temperature heat treatment of
single-wall carbon nanotube bundles in flowing H2
was used to produce a significant fraction (~40%) of diameter-doubled, or
coalesced tubes with a mean diameter corresponding to that of ~(20,20)
tubes. At three laser excitation wavelengths (514.5, 647 and 1064 nm), a
reduction in the Raman scattering intensity of the strong radial and
tangential modes was observed in the H2-treated
sample, consistent with the reduced fraction of tubes in the sample after
coalescence. However, using 488 nm excitation, little or no change is
observed in the Raman spectrum after the
H2-treatment, suggesting that this excitation
wavelength couples only to chiral symmetry tubes. Using the 647 nm
excitation, the effect of H2-treatment on the
tangential band is quite unique, and a significant change in the shape of
the tangential band was observed. Our lineshape analysis, and other
results reported in this issue, suggest that this unique change of shape
is due to lost scattering intensity from metallic tubes partially
compensated by tangential mode scattering from the coalesced tubes. The
normally prominent radial breathing mode band, which would be expected at
~90 cm
indicating that these larger diameter tubes do not exhibit strong resonant
scattering, at least at any of the wavelengths used in this study.
Order No.:
JA809-007 © 1998 MRS
Go to September 1998 Table of Contents
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