Key Takeaways & Executive Findings
- •• • The phonon energy harvesting strategy achieves a photoluminescence (PL) enhancement in WS2 homobilayers by transferring phonon energy from CVD to ME monolayers, with the degree of enhancement regulated by trion or phonon populations. This offers a pathway to mitigate energy dissipation in 2D optoelectronic devices. • • The trion-to-exciton conversion is promoted by the harvested phonon energy, leading to significant PL enhancement. This conversion process is critical for improving the quantum yield of TMD monolayers, which is often limited by trion formation. • • The strategy is universally applicable to different TMD homobilayers, as demonstrated with WS2 and potentially extendable to MoS2 and other TMDs. This universality suggests broad industrial relevance for various 2D material systems. • • The use of defect-induced asymmetry in phonon populations between CVD and ME monolayers enables directional phonon transfer. This asymmetry is key to the energy harvesting mechanism and can be engineered through material synthesis and stacking.
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Abstract
Phonon management in van der Waals (vdW) layered materials has become an area of increasing demand, driven by rapid advancements in electronic and optoelectronic devices. A fundamental challenge in the phonon management of these materials is the effective harvesting of phonons between layers to minimize energy dissipation. Here, we demonstrate a novel phonon energy harvesting strategy in vertically stacked transition metal dichalcogenide (TMD) homobilayers, whose constituent monolayers are prepared individually by mechanical exfoliation (ME) and chemical vapor deposition (CVD) methods. In these systems, owing to the defect-induced asymmetry of phonon populations between layers, the phonon energy can be transferred from CVD monolayers to ME monolayers and then sufficiently utilized to promote the trion-to-exciton conversion in homobilayers for significant photoluminescence (PL) enhancement. The degree of such PL enhancement can be further regulated by varying either the trion or phonon populations involved in the conversion process. This strategy is universally applicable to different TMD homobilayers, presenting a new avenue for phonon energy harvesting in vdW layered materials.
1. Introduction
Phonon management presents a persistent challenge in the microelectronics industry, due to the increasingly severe heat dissipation problems caused by the continued demand for miniaturization and integration of chip components. While the emergence of two-dimensional (2D) materials over the past two decades offers compelling opportunities for further chip size reduction, it simultaneously introduces significant challenges for phonon management at the nanoscale. Consequently, understanding phonon physics in 2D materials, especially in 2D van der Waals (vdW) structures, has become an emerging topic for developing next-generation electronic and optoelectronic devices to extend Moore's law. Achieving efficient phonon transfer across atomically sharp interfaces and subsequently utilizing the transferred phonon/heat energy are key scientific problems for phonon management with 2D vdW materials.
Recent studies have highlighted the potential of graphene-based vdW heterostructures for enabling interfacial heat transfer, attributed to the pronounced cross-plane transmission of phonon modes at the interface. Further, the efficient interlayer phonon-phonon scattering processes occurring on a picosecond timescale were also found in vertically stacked transition metal dichalcogenide (TMD) heterobilayers, where the same chalcogen atoms on both layers can provide nearly degenerate phonon modes to drive this fast interfacial process. In addition, optical phonon transport distance has been observed to reach 3.34 nm in h-10BN/h-11BN isotopic heterojunctions, and interlayer thermal conductivity in the graphene/WS2 system has been shown to be dominated by phonons with the layer spacing up to 2.11 nm. Moreover, air can mediate interlayer thermal radiation with the layer-gap exceeding 2 nm, and near-field thermal radiation represents a promising approach for interlayer thermal/phonon transport. However, research on interlayer phonon transfer within TMD vdW structures remains limited, and effective strategies for utilizing the harvested phonon/heat energy following the interfacial transfer are largely unexplored.
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XU Zheyuan, CHEN Ying, FU Jinyue, CAO Panfeng, ZHENG Biyuan, XU Boyi, XIE Sheng-Yi, JIANG Ying, PAN Anlian (2025). Lightening the unconventional transition metal dichalcogenide homobilayers via phonon energy harvesting. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3543-0
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Frequently Asked Questions
What is the exact mechanism of phonon transfer from CVD to ME monolayers in the homobilayer?
The mechanism relies on defect-induced asymmetry in phonon populations between the CVD and ME monolayers. The CVD monolayer, with a higher defect density, possesses a greater phonon population. This asymmetry drives phonon energy transfer from the CVD to the ME monolayer, where it promotes trion-to-exciton conversion, resulting in enhanced photoluminescence.
How does the trion-to-exciton conversion contribute to PL enhancement, and what are the quantitative metrics?
The harvested phonon energy dissociates trions into excitons, increasing the exciton population and thus enhancing PL. While the abstract does not provide specific numerical values, the degree of PL enhancement can be regulated by varying trion or phonon populations, indicating a tunable effect. The conversion efficiency is expected to be significant, as evidenced by the observed PL enhancement.
Is this strategy applicable to other TMD homobilayers beyond WS2?
Yes, the strategy is universally applicable to different TMD homobilayers. The abstract states that it is applicable to various TMD homobilayers, suggesting that the underlying mechanism of defect-induced phonon asymmetry and trion-to-exciton conversion can be extended to other TMD systems such as MoS2, MoSe2, and WSe2, provided that appropriate defect engineering is implemented.
What are the potential industrial applications of this phonon energy harvesting strategy?
The strategy can be applied to enhance the performance of optoelectronic devices based on 2D TMDs, such as light-emitting diodes, photodetectors, and lasers, by improving their quantum efficiency and reducing energy dissipation. It also offers a pathway for thermal management in 2D electronic devices, where efficient phonon harvesting can mitigate heat accumulation and improve device reliability.
What are the limitations or challenges for scaling up this approach?
Challenges include precise control of defect density in CVD monolayers, uniform stacking of ME and CVD monolayers over large areas, and reproducibility of the phonon transfer effect. Additionally, the long-term stability of the homobilayers under operational conditions needs to be assessed. Further research is required to optimize the process for industrial-scale fabrication.
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