2023 User Research Highlights
Elastic stiffening induces one-dimensional phonons in thin Ta2Se3  nanowires

Project Summary: Confined transport of energy carriers in low-dimensional materials could induce unusual phenomena, leading to properties promising for various applications. In the past, extensive efforts have been carried out to explore and understand thermal transport through a plethora of two-dimensional (2D) materials, while experimental studies of one-dimensional (1D) transport have been largely limited to earlier studies of thermal transport through single-walled carbon or boron nitride nanotubes. Only very recently, attempts to probe thermal transport in quasi-1D van der Waals (vdW) crystal nanowires have been made, which reveal interesting observations. Recently, Prof. Deyu Li’s group at Vanderbilt University experimentally demonstrated 1D phonon-mediated thermal transport in Ta2Se3 nanowires, which is enabled by a phonon stiffening effect. This conclusion is based on diameter dependent thermal conductivity measurement of the nanowires, with the diameter ranging from ~15 to ~50 nm. Normally the thermal conductivity of (3D) phonons in nanowires would reduce with decreasing diameter. However, in the case of Ta2Se3 nanowires, an unusual increasing trend was found when the diameter is below a certain value (~20 nm) at 300 K. This non-monotonic trend is absent at 50 K. This can only be explained by 1D phonon in the thin nanowires at 300K. The detailed findings are published in Appl. Phys. Lett. 120, 062201 (2022).

2DCC Role: This research resulted from a close collaboration between 2DCC and the external user, Prof. Deyu Li. The nanowires of Ta2Se3 used for this study were obtained from microexfoliation of bulk Ta2Se3 crystals grown using a chemical vapor transport method at the 2DCC Bulk Growth facility.

What Has Been Achieved: Demonstrates 1D phonon-mediated thermal transport in Ta2Se3 nanowires, which is enabled by a phonon stiffening effect.

Importance of the Achievement: This work demonstrate 1D phonons through thermal conductivity measurements on Ta2Se3 nanowires. This result would motivate other researches to explore signatures of 1D phonon transport in other quasi-1D systems.

Unique Feature(s) of the MIP that Enabled this Achievement: Synthesis of high-quality Ta2Se3 single crystals is challenging due to the difficulty in controlling the level of disorders in grown crystals. The 2DCC has developed a protocol to grow Ta2Se3 nanowires with a minimal level of disorders. The close collaboration between the user and the 2DCC synthesis enables this work. 

(If Applicable) Publication:

Zhiliang Pan, Seng Huat Lee, Ke Wang, Zhiqiang Mao and Deyu Li, Appl. Phys. Lett. 120, 062201 (2022). DOI: 10.1063/5.0083980

Acknowledgements: The authors thank the financial support from the National Science Foundation (CBET Nos. 1805924 and 2114278). Support for crystal growth and characterization at Penn State was provided by the National Science Foundation through the Penn State 2D Crystal Consortium-Materials Innovation Platform (2DCC-MIP) under NSF Cooperative Agreement No. DMR-2039351.