Abstract

Knowledge of how heat flows anisotropically in van der Waals (vdW) materials is crucial for thermal management of emerging 2D materials devices and design of novel anisotropic thermoelectric materials. Despite the importance, anisotropic heat transport in vdW materials is yet to be systematically studied and is often presumably attributed to anisotropic speeds of sound in vdW materials due to soft interlayer bonding relative to covalent in-plane networks of atoms. In this work, we investigate the origins of the anisotropic heat transport in vdW materials, through time-domain thermoreflectance (TDTR) measurements and first-principles calculations of anisotropic thermal conductivity of three different phases of MoTe₂. MoTe₂ is ideal for the study due to its weak anisotropy in the speeds of sound. We find that even when the speeds of sound are roughly isotropic, the measured thermal conductivity of MoTe₂ along the c-axis is 5–8 times lower than that along the in-plane axes. We derive meaningful characteristic heat capacity, phonon group velocity, and relaxation times from our first principles calculations for selected vdW materials (MoTe₂, BP, h-BN, and MoS₂), to assess the contributions of these factors to the anisotropic heat transport. Interestingly, we find that the main contributor to the heat transport anisotropy inmore » vdW materials is anisotropy in heat capacity of the dominant heat-carrying phonon modes in different directions, which originates from anisotropic optical phonon dispersion and disparity in the frequency of heat-carrying phonons in different directions. Further, the discrepancy in frequency of the heat-carrying phonons also leads to ~2 times larger average relaxation times in the cross-plane direction, and partially explains the apparent dependence of the anisotropic heat transport on the anisotropic speeds of sound. This work provides insight into understanding of the anisotropic heat transport in vdW materials.« less

Authors:

Li, Hongkun  ^[1];

• Search DOE PAGES for author "Li, Hongkun"
• Search DOE PAGES for ORCID "0000-0001-7094-4793"

Pandey, Tribhuwan  ^[2];

• Search DOE PAGES for author "Pandey, Tribhuwan"
• Search DOE PAGES for ORCID "0000-0002-0373-7716"

Jiang, Yi  ^[3];

• Search DOE PAGES for author "Jiang, Yi"
• Search DOE PAGES for ORCID "0000-0002-0099-8611"

Gu, Xiaokun  ^[4];

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• Search DOE PAGES for ORCID "0000-0003-3803-3951"

Lindsay, Lucas  ^[5];

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• Search DOE PAGES for ORCID "0000-0001-9645-7993"

Koh, Yee Kan  ^[3]

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• Search DOE PAGES for ORCID "0000-0002-4156-6209"

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+ Show Author Affiliations

1. National Univ. of Singapore (Singapore); Southwest Jiaotong University, Chengdu (China)
2. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Univ. of Antwerp (Belgium)
3. National Univ. of Singapore (Singapore)
4. Shanghai Jiao Tong Univ. (China)
5. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Publication Date:

Wed Aug 09 00:00:00 EDT 2023

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE); Singapore Ministry of Education; USDOE

OSTI Identifier:

1999048

Alternate Identifier(s):

OSTI ID: 1997311

Grant/Contract Number:  

AC05-00OR22725; MOE2019-T2-2-135; AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Materials Today Physics

Additional Journal Information:

Journal Volume: 37; Journal ID: ISSN 2542-5293

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; anisotropic thermal conductivity; van der Waals materials; anisotropy in effective heat capacity; anisotropic effective relaxation time; anisotropic speeds of sound