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Extraordinary thermal conductivity of polyvinyl alcohol composite by aligning densified carbon fiber via magnetic field
Nano Research 2023, 16 (2): 2572-2578
Published: 23 November 2022
Downloads:117

Thermal interface materials (TIMs) with high through-plane thermal conductivity are urgently desired to avoid overheating of high-power density electronics. Introducing and aligning fillers in polymer matrixes via magnetic field is a promising method to improve the thermal conductivity of the polymer. However, either the fillers need to be modified with magnetic particles or a strong magnetic field is needed for good alignment in high filler content. This prevents further improvement of the through-plane thermal conductivity. Herein, mesophase pitch-based carbon fibers (MPCFs) with a content as high as 76 wt.% are aligned vertically in water-soluble polyvinyl alcohol (PVA) under a low magnetic field (~ 0.4 T), forming a vertically aligned MPCF (VAMPCF)/PVA composite with an extraordinary through-plane thermal conductivity of 86 W/(m·K), which is higher than that of many alloys. In addition, both theoretical and experimental results demonstrate that the critical intensity of the magnetic field needed for good alignment of the fillers depends on their size and magnetic susceptibility. Furthermore, the water solubility of PVA makes it easy to recycle MPCFs. This study offers an inspired venue to develop excellent and eco-friendly TIMs to meet ever increasing demand in heat dissipation for electronics.

Research Article Issue
Highly anisotropic thermal conductivity of few-layer CrOCl for efficient heat dissipation in graphene device
Nano Research 2022, 15 (10): 9377-9385
Published: 23 July 2022
Downloads:69

With the packing density growing continuously in integrated electronic devices, sufficient heat dissipation becomes a serious challenge. Recently, dielectric materials with high thermal conductivity have brought insight into effective dissipation of waste heat in electronic devices to prevent them from overheating and guarantee the performance stability. Layered CrOCl, an anti-ferromagnetic insulator with low-symmetry crystal structure and atomic level flatness, might be a promising solution to the thermal challenge. Herein, we have systematically studied the thermal transport of suspended few-layer CrOCl flakes by micro-Raman thermometry. The CrOCl flakes exhibit high thermal conductivities along zigzag direction, from ~ 392 ± 33 to ~ 1,017 ± 46 W·m−1·K−1 with flake thickness from 2 to 50 nm. Besides, pronounced thickness-dependent thermal conductivity ratio ( κZZ/ κAR from ~ 2.8 ± 0.24 to ~ 4.3 ± 0.25) has been observed in the CrOCl flakes, attributed to the discrepancy of phonon dispersion and phonon surface scattering. As a demonstration to the heat sink application of layered CrOCl, we then investigate the energy dissipation in graphene devices on CrOCl, SiO2 and hexagonal boron nitride (h-BN) substrates, respectively. The graphene device temperature rise on CrOCl is only 15.4% of that on SiO2 and 30% on h-BN upon the same electric power density, indicating the efficient heat dissipation of graphene device on CrOCl. Our study provides new insights into two-dimentional (2D) dielectric material with high thermal conductivity and strong anisotropy for the application of thermal management in electronic devices.

Research Article Issue
Highly in-plane anisotropy of thermal transport in suspended ternary chalcogenide Ta2NiS5
Nano Research 2022, 15 (7): 6601-6606
Published: 04 May 2022
Downloads:66

Energy dissipation has always been an attention-getting issue in modern electronics and the emerging low-symmetry two-dimensional (2D) materials are considered to have broad prospects in solving the energy dissipation problem. Herein the thermal transport of a typical 2D ternary chalcogenide Ta2NiS5 is investigated. For the first time we have observed strongly anisotropic in-plane thermal conductivity towards armchair and zigzag axes of suspended few-layer Ta2NiS5 flakes through Raman thermometry. For 7-nm-thick Ta2NiS5 flakes, the κzigzag is 4.76 W·m−1·K−1 and κarmchair is 7.79 W·m−1·K−1, with a large anisotropic ratio ( κarmchair/κzigzag) of 1.64 mainly ascribed to different phonon mean-free-paths along armchair and zigzag axes. Moreover, the thickness dependence of thermal anisotropy is also discussed. As the flake thickness increases, the κarmchair/κzigzag reduces sharply from 1.64 to 1.07. This could be attributed to the diversity in phonon boundary scattering, which decreases faster in zigzag direction than in armchair direction. Such anisotropic property enables heat flow manipulation in Ta2NiS5 based devices to improve thermal management and device performance. Our work helps reveal the anisotropy physics of ternary transition metal chalcogenides, along with significant guidance to develop energy-efficient next generation nanodevices.

Research Article Issue
Anisotropic in-plane thermal conductivity for multi-layer WTe2
Nano Research 2022, 15 (1): 401-407
Published: 01 June 2021
Downloads:71

Improving thermal transport between substrate and transistors has become a vital solution to the thermal challenge in nanoelectronics. Recently 2D WTe2 has sparked extensive interest because of heavy atomic mass and low Debye temperature. Here, the thermal transport of supported WTe2 was studied via Raman thermometry with electrical heating. The supported 30 nm WTe2 encased with 70 nm Al2O3 delivered 4.8 W·m-1·K-1 in-plane thermal conductivity along zigzag direction at room temperature, which was almost 1.6 times larger than that along armchair direction (3.0 W·m-1·K-1). Interestingly, the superior and inferior directions for thermal transport are just opposite of those for electrical transport. Hence, a heat manipulation model in WTe2 FET device was proposed. Within the designed configuration, waste heat in WTe2 would be mostly dissipated to metal contacts located along zigzag, relieving the local temperature discrepancy in the channel effectively and preventing degradation or breakdown. Our study provides new insight into thermal transport of anisotropic 2D materials, which might inspire energy-efficient nanodevices in the future.

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