Observation of highly viscous heat transport in ultrathin layered semiconductors at room temperature

For a host of applications it is crucial to understand and control heat dissipation. This is particularly true for transistors and interconnects, which are playing crucial roles in information and communication technologies. These are applications where 2D materials could play an important role in the future. Therefore, it is crucial to understand heat transport in these materials.

We have recently developed a novel experimental technique to follow heat diffusion in thin films directly in space and time, and have applied this technique to the 2D layered materials of the type transition metal dichalcogenide (TMD), specifically MoSe₂, MoS₂, WSe₂ and WS₂ [1]. For flakes with a thickness around 15 nm, our spatiotemporal pump-probe thermometry technique gives diffusivities that agree well with both experimentally obtained thermal conductivities in literature and with ab-initio calculations of the thermal diffusivities of these materials [1,2]. For these flakes, heat transport follows Fourier’s law of diffusion.

Interestingly, we observe the occurrence of highly viscous heat transport, with strongly reduced thermal diffusivities, for ultrathin suspended TMD flakes at room temperature [3]. We attribute this observation to the combination of hydrodynamic and thermoelastic effects, which constitutes a novel “hydro-thermoelastic” regime of non-diffusive transport. Our fit-parameter-free mesoscopic model of these combined effects reproduces the experimental results.

The identification of non-diffusive heat transport at room temperature opens up interesting new pathways towards thermal management and thermoelectric energy generation based on ultrathin layered semiconductors.

[1] S. Varghese et al, Rev. Sci. Instr. 94 (2023), 034903

[2] D. Saleta Reig et al, Adv. Mater. 34 (2022), 2108352

[3] S. Varghese et al. to be submitted