The degree of thermal
anisotropy affects critically key device-relevant
properties of layered two-dimensional materials. Here, we systematically
study the in-plane and cross-plane thermal conductivity of crystalline
SnSe2 films of varying thickness (16–190 nm) and
uncover a thickness-independent thermal conductivity anisotropy ratio
of about ∼8.4. Experimental data obtained using Raman thermometry
and frequency domain thermoreflectance showed that the in-plane and
cross-plane thermal conductivities monotonically decrease by a factor
of 2.5 with decreasing film thickness compared to the bulk values.
Moreover, we find that the temperature-dependence of the in-plane
component gradually decreases as the film becomes thinner, and in
the range from 300 to 473 K it drops by more than a factor of 2. Using
the mean free path reconstruction method, we found that phonons with
MFP ranging from ∼1 to 53 and from 1 to 30 nm contribute to
50% of the total in-plane and cross-plane thermal conductivity, respectively.