  Thermal transport in the Si/SiO$_2$ multishell nanotubes is investigated
theoretically. The phonon energy spectra are obtained using the atomistic
Lattice Dynamics approach. Thermal conductivity is calculated using the
Boltzmann transport equation within the relaxation time approximation.
Redistribution of the vibrational spectra in multishell nanotubes leads to a
decrease of the phonon group velocity and the thermal conductivity as compared
to homogeneous Si nanowires. Phonon scattering on the Si/SiO$_2$ interfaces is
another key factor of strong reduction of the thermal conductivity in these
structures (down to 0.2 W/mK at room temperature). We demonstrate that phonon
thermal transport in Si/SiO$_2$ nanotubes can be efficiently suppressed by a
proper choice of nanotube's geometrical parameters: lateral cross-section,
thickness and number of shells.
