Improved Thermal Anisotropy of Multi-Layer Tungsten Telluride on Silicon Substrate.

WTe 2 , a low-symmetry transition metal dichalcogenide, has broad prospects in functional device applications due to its excellent physical properties. When WTe 2 flake is integrated into practical device structures, its anisotropic thermal transport could be affected greatly by the substrate, which matters a lot to the energy efficiency and functional performance of the device. To investigate the effect of SiO 2 /Si substrate, we carried out a comparative Raman thermometry study on a 50 nm-thick supported WTe 2 flake (with κ zigzag = 62.17 W·m -1 ·K -1 and κ armchair = 32.93 W·m -1 ·K -1 ), and a suspended WTe 2 flake of similar thickness (with κ zigzag = 4.45 W·m -1 ·K -1 , κ armchair = 4.10 W·m -1 ·K -1 ). The results show that the thermal anisotropy ratio of supported WTe 2 flake (κ zigzag /κ armchair ≈ 1.89) is about 1.7 times that of suspended WTe 2 flake (κ zigzag /κ armchair ≈ 1.09). Based on the low symmetry nature of the WTe 2 structure, it is speculated that the factors contributing to thermal conductivity (mechanical properties and anisotropic low-frequency phonons) may have affected the thermal conductivity of WTe 2 flake in an uneven manner when supported on a substrate. Our findings could contribute to the 2D anisotropy physics and thermal transport study of functional devices based on WTe 2 and other low-symmetry materials, which helps solve the heat dissipation problem and optimize thermal/thermoelectric performance for practical electronic devices.