Thickness-Dependent Ultralow In-Plane Thermal Conductivity of Chemical Vapor-Deposited SnSe₂ Nanofilms: Implications for Thermoelectrics

Tin diselenide (SnSe2) as a two-dimensional semiconductor material shows great potential in nanoscale electronics, optoelectronics, and thermoelectric applications; however, much is unclear about its thermal properties. Here, we systematically measure the in-plane thermal conductivity of suspended few-layer chemical vapor deposition (CVD)-grown SnSe2 nanofilms using refined optothermal micro-Raman method. The lateral size dependence and thickness dependence of the in-plane thermal conductivity of SnSe2 nanofilms are also investigated. The measured in-plane thermal conductivity of the suspended SnSe2 nanofilms varies from 1.80 ± 0.16 to 2.90 ± 0.15 W/mK when the number of atomic layers increases from 5 layers (5L) to 15L. This tendency mainly originates from the reduced phonon-boundary scattering with increased thickness and a short phonon mean-free-path (MFP) of 5–10 nm in CVD-grown SnSe2 nanofilms, which agrees well with the Fuchs–Sondheimer model. Moreover, the in-plane thermal conductivity of 15L SnSe2 suspended over holes with diameters varying from 3 to 6 μm shows no obvious in-plane size dependence; this can be attributed to its much smaller phonon MFP (5–10 nm) compared to the diameter of the holes. Our study gives insights into the basic thermal transport properties of polycrystalline SnSe2 nanofilms, supporting future studies of this nanomaterial for thermoelectric applications.