(
)
M.L. TerranoÕa et al.rChemical Physics Letters 327 2000 284–290
289
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x
otubes 30 and to explain this fundamental issue
some hypothesis have been raised. It has been argued
that chemisorption of carbon on the surface of transi-
tion metals would help in modifying the orientation
of carbon p-orbitals and in producing curvature ef-
conditions generated SWCNs belonging prevalently
Ž
.
to the n,0 achiral symmetry subclass. However,
some preliminary results of experiments still in
progress suggest that a different choice of process
parameters can favor the selective formation of nan-
otubes with a different geometry.
w
x
fects in flat graphene structures 31 . It has been also
observed that stabilization of C dangling bonds by
metal atoms inhibits tube closure and formation of
fullerene-like molecules 6,32,33 . It should be em-
phasized, however, that the theory of SWCNs growth
is still under discussion, and no exhaustive interpre-
tation of the role played by the metals has still been
given.
In this context, the feasibility of the presented
methodology to synthesize in an effective way sin-
gle-walled carbon might be used to explore its poten-
tiality for the large scale production of SWCN with
selected tubular configuration.
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x
The present results indicates that the presence of
Fe, Ni or Co metals in form of submicrometer-sized
particles is necessary also for SWCNs growth by our
technique employing nanographite and atomic hy-
drogen as C feedstock and reactants, respectively.
Bonding of carbon species, produced by H-etching,
to the metal coordination sites is thought to reduce
localized C supersaturation and to avoid formation of
thick carbon clusters and subsequent coalescence
into graphite layers, as experienced when the pro-
cesses were carried out in the absence of a supported
metallic catalyst.
Acknowledgements
Ž
The authors are indebted to Dr. Ruani CNR,
.
Ž
.
Bologna and A. Tagliapietra Renishaw, Italy for
the Raman spectra.
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