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Materials Science Division |
HighlightsElectron Diffraction on Single-walled Carbon NanotubesElectron Diffraction on Single-walled Carbon Nanotubes Scientific Achievement We
have performed a comparative
study of the helicity distribution of single-walled carbon nanotubes
(C-SWNTs)
synthesized by different CVD processes in order to understand how the
synthesis
conditions can influence and control their growth mechanism. To achieve this aim, we
used the nano-beam electron
diffraction mode, employing a parallel
probe of about 50
nm, which is able to inspect individual tubes.
According to luminescence and Raman spectroscopies, these
tubes are
expected to display a narrow distribution of helicities. However these techniques
fail for detecting
helicities of conducting tubes, which can be one third of the tubes
present in
a sample. On the
other hand, electron
diffraction has been shown to be the most reliable technique for
obtaining the
complete determination of the atomic structure (chiral angle and
diameter) of
individual nanotubes. We
recorded the intensities of
electron diffraction patterns (EDPs) from individual SW-CNTs as well as
from
bundles of CNTs, using two different FEI Tecnai F20 TEMs operating at
100 and
120 keV respectively. In
the case of
individual SWNTs, their chiral indices were determined as the best
value
fitting experimental and simulated patterns calculated using
kinematical
electron theory. We
have developed a comparative
analysis of a significant number of NTs (>50) synthesized by two
different
CVD techniques: a thermal CVD process for which catalyst particles are
prepared
ex situ using a colloidal technique and deposited on
the substrate and a
hot filament CVD process where catalyst particles are prepared in
situ
by heating, under hydrogen gas, a few monolayers of the catalytic metal
deposited on the substrate. In
both
cases, the substrates were perforated silica membranes, making it
possible to
acquire EDPs from suspended nanotubes. Significance The
determination of the
helicity distribution of carbon
single-walled nanotubes (C-SWNTs) is crucial in order to better
understand
their growth mechanism and, as a long-term goal, to control their
atomic
arrangement. This
point is very
important since the electronic properties of these NTs are strongly
correlated
with this aspect. In
this work we
studied by electron diffraction the chiral angle distribution from
different
samples of C-SWNTs synthesized by two different CVD techniques. This
work has been presented
in five different international meetings
during 2007 and 2008.
We have
submitted a paper to Surface Science and we are
preparing another paper
that will compile the main results coming from this work. Performers 
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