  Understanding the kinetic selectivity of carbon nanotube growth at the scale
of individual nanotubes is essential for the development of high chiral
selectivity growth methods. Here we demonstrate that homodyne polarization
microscopy can be used for high-throughput imaging of long individual carbon
nanotubes under real growth conditions (at ambient pressure, on a substrate),
and with sub-second time resolution. Our in situ observations on hundreds of
individual nanotubes reveal that about half of them grow at a constant rate all
along their lifetime while the other half exhibits stochastic changes in growth
rates, and switches between growth, pause and shrinkage. Statistical analysis
shows that the growth rate of a given nanotube essentially varies between two
values, with similar average ratio (~1.7) regardless of whether the rate change
is accompanied by a change in chirality. These switches indicate that the
nanotube edge or the catalyst nanoparticle fluctuates between different
configurations during growth.
