Abstract
The densification of integrated circuits requires thermal management strategies and high thermal conductivity materials1–3. Recent innovations include the development of materials with thermal conduction anisotropy, which can remove hotspots along the fast-axis direction and provide thermal insulation along the slow axis4,5. However, most artificially engineered thermal conductors have anisotropy ratios much smaller than those seen in naturally anisotropic materials. Here we report extremely anisotropic thermal conductors based on large-area van der Waals thin films with random interlayer rotations, which produce a room-temperature thermal anisotropy ratio close to 900 in MoS2, one of the highest ever reported. This is enabled by the interlayer rotations that impede the through-plane thermal transport, while the long-range intralayer crystallinity maintains high in-plane thermal conductivity. We measure ultralow thermal conductivities in the through-plane direction for MoS2 (57 ± 3 mW m−1 K−1) and WS2 (41 ± 3 mW m−1 K−1) films, and we quantitatively explain these values using molecular dynamics simulations that reveal one-dimensional glass-like thermal transport. Conversely, the in-plane thermal conductivity in these MoS2 films is close to the single-crystal value. Covering nanofabricated gold electrodes with our anisotropic films prevents overheating of the electrodes and blocks heat from reaching the device surface. Our work establishes interlayer rotation in crystalline layered materials as a new degree of freedom for engineering-directed heat transport in solid-state systems.
Highlights
To design materials with higher ρ that are suitable for real-world applications, an approach needs to be developed to include three key features: (1) a candidate material with intrinsically high κf, usually one with efficient phonon-mediated thermal transport; (2) a method to substantially reduce κs without affecting κf; and (3) facile, scalable production and integration of such a material with precise control of the material dimensions
The films are produced in large-scale using two steps: wafer-scale growth of continuous transition metal dichalcogenides (TMDs) monolayers and layer-by-layer stacking in vacuum using previously reported methods[19,20]
A stream of laser pulses heats up the surface of an Al pad deposited on an r-TMD film on sapphire and produces a temperature-sensitive thermoreflectance signal (−Vin/Vout in Fig. 2a), which is measured with a probe pulse after a varying time delay
Summary
Shi En Kim[1], Fauzia Mujid[2], Akash Rai[3], Fredrik Eriksson[4], Joonki Suh[2,5], Preeti Poddar[2], Ariana Ray[6], Chibeom Park[1,5], Erik Fransson[4], Yu Zhong[2], David A. We report extremely anisotropic thermal conductors based on large-area van der Waals thin films with random interlayer rotations, which produce a room-temperature thermal anisotropy ratio close to 900 in MoS2, one of the highest ever reported. This is enabled by the interlayer rotations that impede the through-plane thermal transport, while the long-range intralayer crystallinity maintains high in-plane thermal conductivity. Layered van der Waals (vdW) materials such as graphite and transition metal dichalcogenides (TMDs) provide an ideal material platform for designing such high-ρ materials They generally have excellent intrinsic in-plane thermal conductivities (κ||) in single-crystalline form. One currently missing capability is an approach for significantly decreasing the out-of-plane thermal conductivity (κ⊥) while maintaining high κ||
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