  There has been great interest in two-dimensional materials, beyond graphene,
for both fundamental sciences and technological applications. Silicene, a
silicon counterpart of graphene, has been shown to possess some better
electronic properties than graphene. However, its thermal transport properties
have not been fully studied. In this paper, we apply the first-principles-based
phonon Boltzmann transport equation to investigate the thermal conductivity of
silicene as well as the phonon scattering mechanisms. Although both graphene
and silicene are two-dimensional crystals with similar crystal structure, we
find that phonon transport in silicene is quite different from that in
graphene. The thermal conductivity of silicene shows a logarithmic increase
with respect to the sample size due to the small scattering rates of acoustic
in-plane phonon modes, while that of graphene is finite. Detailed analysis of
phonon scattering channels shows that the linear dispersion of the acoustic
out-of-plane (ZA) phonon modes, which is induced by the buckled structure,
makes the long-wavelength longitudinal acoustic (LA) phonon modes in silicene
not as efficiently scattered as that in graphene. Compared with graphene, where
most of the heat is carried by the acoustic out-of-plane (ZA) phonon modes, the
ZA phonon modes in silicene only have ~10% contribution to the total thermal
conductivity, which can also be attributed to the buckled structure. This
systematic comparison of phonon transport and thermal conductivity of silicene
and graphene using the first-principle-based calculations shed some light on
other two-dimensional materials, such as two-dimensional transition metal
dichalcogenides.
