  The phonon thermal conductivity in diamond nanowires (DNW) is studied by
molecular dynamics simulation. It is found that the thermal conductivity in
narrower DNW is lower and does not show obvious temperature dependence; a very
small value (about 2.0 W/m/K) of thermal conductivity is observed in
ultra-narrow DNW, which may be of potential applications in thermoelectric
devices. These two phenomena are probably due to the dominant surface effect
and phonon confinement effect in narrow DNW. Our simulation reveals a high
anisotropy in the heat transport of DNW. Specifically, the thermal conductivity
in DNW along [110] growth direction is about five times larger than that of
[100] and [111] growth directions. The anisotropy is believed to root in the
anisotropic group velocity for acoustic phonon modes in DNW along three
different growth directions.
