Phonon dynamics and thermal conductivity of PtSe2 thin films: Impact of crystallinity and film thickness on heat dissipation

TL;DR

This study investigates how crystallinity and thickness affect phonon behavior and thermal conductivity in PtSe2 thin films, revealing key insights into heat transport mechanisms relevant for 2D electronic and thermoelectric applications.

Contribution

It provides a comprehensive experimental and theoretical analysis of phonon dynamics and thermal conductivity in PtSe2, highlighting the impact of crystallinity and film thickness on heat dissipation.

Findings

Polycrystalline films >12 nm show 35% lower cross-plane thermal conductivity than crystalline films.

Ballistic heat transport persists up to ~20 nm thickness in PtSe2.

Layer-dependent phonon velocities range from 1340 to 1873 m/s.

Abstract

We present a comparative investigation of the influence of crystallinity and film thickness on the acoustic and thermal properties of 2D layered PtSe2 thin films of varying thickness (0.6-24 nm) by combining a set of experimental techniques, namely, frequency domain thermo-reflectance, low-frequency Raman and pump-probe coherent phonon spectroscopy. We find a 35% reduction in the cross-plane thermal conductivity of polycrystalline films with thickness larger than 12 nm compared to the crystalline films of the same thickness due to phonon grain boundary scattering. Density functional theory calculations are in good agreement with the experiments and further reveal the ballistic nature of cross-plane heat transport in PtSe2 up to a certain thickness (~20 nm). In addition, our experiments revealed strong interlayer interactions in PtSe2, short acoustic phonon lifetimes in the range of picoseconds, out-of-plane elastic constant C33=31.8 GPa and layer-dependent group velocity ranging from 1340 m/s in bilayer PtSe2 to 1873 m/s in 8 layers of PtSe2. The potential of tuning the lattice cross-plane thermal conductivity of layered 2D materials with the level of crystallinity and the real-time observation of coherent phonon dynamics, which have direct implications on the cooling and transport of electrons, open a new playground for research in 2D thermoelectric devices and provide guidelines for thermal management in 2D electronics.