Thermal conductivity of exfoliated and chemical vapor deposition-grown tin disulfide nanofilms: role of grain boundary conductance

Tin disulfide (SnS2) is a layered two-dimensional (2D) semiconductor material that shows great potentials in applications such as photodetectors, sensors, field-effect transistors, thermoelectric power generators, etc. The understanding of thermal transport in SnS2 is important for the optimization of thermal management and energy transport and conversion processes in these devices. Here we compare the in-plane thermal conductivities of mechanically exfoliated single-crystalline and chemical vapor deposition (CVD)grown polycrystalline SnS2 nanofilms measured using the Raman optothermal technique. The polycrystalline SnS2 film with a grain size of 250 nm has a low in-plane thermal conductivity of 4.8-5.6 W m K-1, which is approximately half that of the single-crystalline SnS2 film due to phonon scattering at the grain boundaries. The thermal transport across crystal grains is simulated using two approaches: (1) A finite element model with generated Voronoi cells, and (2) an empirical equation that takes into account the grain boundary thermal conductance (G'). The two approaches yield similar values for the effective G', as well as consistent dependences of the in-plane thermal conductivity on the average grain size. It is predicted that the in-plane thermal conductivity of the polycrystalline SnS2 film can be substantially reduced with finer grains. The results of this work offer a fundamental understanding of the thermal transport properties of single-crystalline and polycrystalline SnS2 films from different growth methods, and demonstrate the potential to control the thermal conductivity of SnS2 by tuning the grain size for future thermoelectric applications. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study reveals that the thermal conductivity of polycrystalline SnS2 film is lower, approximately half that of single-crystalline SnS2 film, mainly due to phonon scattering at grain boundaries. Two simulation approaches suggest that thermal transport across crystal grains leads to the reduction of thermal conductivity, therefore, the thermal conductivity of polycrystalline SnS2 film can be substantially reduced by tuning the grain size.