  We use molecular dynamics simulations to examine the phonon lifetimes in
(10,10) carbon nano-tubes (CNTs), both when isolated and when supported on
amorphous SiO2 substrates. We deter-mine the Umklapp, normal, boundary and
CNT-substrate phonon scattering rates from the com-puted inverse lifetimes.
Suspended CNTs have in-plane optical phonon lifetimes between 0.7-2 ps,
consistent with recent experiments, but contact with the substrate leads to a
lifetime reduction to the 0.6-1.3 ps range. The thermal conductivity of the
supported CNT is also computed to be ~30 percent lower than that of the
isolated CNT. The thermal boundary conductance estimated from the CNT-substrate
phonon scattering rates is in good agreement with that computed from the
Green-Kubo relation and with previous experimental results. The results
highlight that solid substrates can strongly affect and could be even used to
tune the thermal properties of CNTs.
