Room-temperature Raman detection of all Davydov components of <inline-formula><tex-math id="Z-20250926165500">\begin{document}${\mathrm{A}}_1' $\end{document}</tex-math></inline-formula> mode in transition metal dichalcogenides

LI Linhan; MEI Rui; LIU Xuelu; LIN Miaoling; TAN Pingheng

doi:10.7498/aps.74.20250960

Abstract

A comprehensive van der Waals heterostructure strategy has been implemented to be able to observe all Davydov components of the A-mode in few-layer transition-metal dichalcogenides (TMDs) at room temperature. In few-layer 2H-TMDs such as MoS₂, MoSe₂, and WS₂, the A-mode phonon splits into N Davydov components that directly reflect the interlayer coupling strength and layer number. Under the resonance conditions near the band edge, however, strong photoluminescence (PL) and band filling effects severely obscure these Raman signals, particularly for infrared-active modes, rendering the observation of all the Davydov components at ambient temperature infeasible. In this work, few-layer (1–4 layers) TMD flakes are mechanically exfoliated and dry-transferred onto four-layer graphene, followed by high-vacuum annealing to improve the interfacial coupling quality. Ultralow-frequency Raman spectra of interlayer shear and breathing modes provide an unambiguous fingerprint for determining the layer numbers of both TMDs and graphene constituents, while differential reflectance spectra precisely determine the resonance energies of excitons.Under resonance excitation with the A-exciton, the heterostructures exhibit a marked enhancement of A-mode Raman intensity accompanied by strong PL quenching. Raman peaks associated with all the Davydov components are simultaneously resolved for MoS₂, MoSe₂, and WS₂ at room temperature. The activation of all the Davydov components arises from three synergistic mechanisms: 1) symmetry breaking at the TMDs/graphene interface, which renders the forbidden components Raman-allowed; 2) interfacial charge transfer, which suppresses the PL background by depleting photoexcited carriers entering into graphene; and 3) efficient nonradiative relaxation pathways provided by graphene, which mitigates the band filling effect and restore resonant Raman scattering. Furthermore, the highest-frequency Davydov component A(1) exhibits an overall blue shift in the heterostructure relative to the intrinsic TMDs, with the magnitude of the shift decreasing as the layer number increases. This behavior can be explained by a diatomic linear-chain model in which interfacial van der Waals coupling enhances the force constants of intralayer vibrations.This work thus establishes a general platform for Raman analysis of all the Davydov components of the A mode in two-dimensional (2D) TMDs at room temperature and elucidates how interface coupling, layer number, and symmetry breaking jointly govern phonon behavior. The approach offers valuable insights into phonon engineering and interface design in 2D heterostructures and may readily be extended to relevant systems such as WSe₂ and ReS₂.

Keywords:

Authors and contacts

1.
State Key Laboratory of Semiconductor Physics and Chip Technologies, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
2.
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China

Corresponding author: TAN Pingheng, phtan@semi.ac.cn

Funds: Project supported by the National Key R&D Program of China (Grant No. 2022YFF0609800) and the National Natural Science Foundation of China (Grant Nos. 12127807, 12322401, 12393832).

[1]	Splendiani A, Sun L, Zhang Y, Li T, Kim J, Chim C Y, Galli G, Wang F 2010 Nano Lett. 10 1271 Google Scholar
[2]	Wang G, Chernikov A, Glazov M M, Heinz T F, Marie X, Amand T, Urbaszek B 2018 Rev. Mod. Phys. 90 021001 Google Scholar
[3]	Zhang X, Qiao X F, Shi W, Wu J B, Jiang D S, Tan P H 2015 Chem. Soc. Rev. 44 2757 Google Scholar
[4]	Song Q J, Tan Q H, Zhang X, Wu J B, Sheng B W, Wan Y, Wang X Q, Dai L, Tan P H 2016 Phys. Rev. B 93 115409 Google Scholar
[5]	Leng Y C, Lin M L, Zhou Y, Wu J B, Meng D, Cong X, Li H, Tan P H 2021 Nanoscale 13 9732 Google Scholar
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[19]	Zhang X, Han W P, Wu J B, Milana S, Lu Y, Li Q Q, Ferrari A C, Tan P H 2013 Phys. Rev. B 87 115413 Google Scholar
[20]	Tan P H, Han W P, Zhao W J, Wu Z H, Chang K, Wang H, Wang Y F, Bonini N, Marzari N, Pugno N, Savini G, Lombardo A, Ferrari A C 2012 Nat. Mater. 11 294 Google Scholar
[21]	Wu J B, Zhang X, Ijäs M, Han W P, Qiao X F, Li X L, Jiang D S, Ferrari A C, Tan P H 2014 Nat. Commun. 5 5309 Google Scholar
[22]	Liang L, Zhang J, Sumpter B G, Tan Q H, Tan P H, Meunier V 2017 ACS Nano 11 11777 Google Scholar
[23]	Pierucci D, Henck H, Avila J, Balan A, Naylor C H, Patriarche G, Dappe Y J, Silly M G, Sirotti F, Johnson A T C, Asensio M C, Ouerghi A 2016 Nano Lett. 16 4054 Google Scholar
[24]	Bieniek M, Szulakowska L, Hawrylak P 2020 Phys. Rev. B 101 125423 Google Scholar
[25]	Robert C, Han B, Kapuscinski P, Delhomme A, Faugeras C, Amand T, Molas M R, Bartos M, Watanabe K, Taniguchi T, Urbaszek B, Potemski M, Marie X 2020 Nat. Commun. 11 4037 Google Scholar
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Cited By

图 1 本征MoS₂中A模的Davydov组分　(a) 1—4L TMDs中A模所有Davydov组分原子位移示意图; (b) 本征1—4LM的差分反射谱; (c) 本征1—4LM的低频模; (d) 本征1—4LM中A模的Davydov组分缺失

Figure 1. Davydov components of A-mode in intrinsic MoS₂: (a) Schematic diagram of atomic displacements for all the Davydov components of A-mode in 1–4L TMDs; (b) differential reflectance spectra of intrinsic 1–4LM; (c) low-frequency modes of intrinsic 1–4LM; (d) failure to observe all the Davydov components of A-mode in intrinsic 1–4LM.

DownLoad: Full-Size Img PowerPoint

图 2 MoS₂/石墨烯异质结的层间耦合与拉曼增强机制　(a) 低频模: nLM/4LG vs. 本征nLM; (b) 高频模: nLM/4LG vs. 本征n LM; (c) PL谱: nLM/4LG vs. 本征nLM. 一阶拉曼增强机制　(d1), (d2) 1LM/4LG vs. 本征1LM; (e1), (e2) nLM/4LG vs. 本征nLM, $ n \geqslant 2 $

Figure 2. Interlayer coupling and Raman enhancement mechanism in MoS₂/Gr heterostructures: (a) Low-frequency modes: nLM/4LG vs. intrinsic nLM; (b) high-frequency modes: nLM/4LG vs. intrinsic nLM; (c) PL spectra: nLM/4LG vs. intrinsic nLM. Mechanism of first-order Raman enhancement: (d1), (d2) 1LM/4LG vs. intrinsic 1LM; (e1), (e2) nLM/4LG vs. intrinsic nLM, $ n \geqslant 2 $.

DownLoad: Full-Size Img PowerPoint

图 3 MoS₂/石墨烯异质结中A模的Davydov组分　(a)—(d) 1—4LM/4LG的Davydov组分(室温); (e)—(h) 各组分峰强随激发光能量的变化(1—4LM/4LG)

Figure 3. Davydov components of A-mode in MoS₂/Gr heterostructures: (a)–(d) Davydov components in 1–4LM/4LG (room temperature); (e)–(h) Excitation energy dependence of component peak intensities (1–4LM/4LG).

DownLoad: Full-Size Img PowerPoint

图 4 异质结策略的跨材料普适性　(a)—(d) MoSe₂体系与(e)—(h) WS₂体系中的Davydov组分观测

Figure 4. Universality of heterostructure strategies. Observation of Davydov components in (a)–(d) MoSe₂ system and (e)–(h) WS₂ system

DownLoad: Full-Size Img PowerPoint

图 5 A(1)模频率的层数依赖关系　(a)—(c) 本征nL MoS₂, nL MoSe₂, nL WS₂样品中A(1)模频率随层数的变化(蓝色菱形); nL MoS₂/4LG, nL MoSe₂/4LG, nL WS₂/4LG异质结样品中A(1)模频率随层数的变化(红色圆形)

Figure 5. Dependence of the Raman peak of A(1) mode on the number of layers (a)–(c) in intrinsic nL MoS₂, nL MoSe₂, nL WS₂ (blue diamond) and in nL MoS₂/4LG, nL MoSe₂/4LG, nL WS₂/4LG heterstructures (red dot).

DownLoad: Full-Size Img PowerPoint

[1]	Splendiani A, Sun L, Zhang Y, Li T, Kim J, Chim C Y, Galli G, Wang F 2010 Nano Lett. 10 1271 Google Scholar
[2]	Wang G, Chernikov A, Glazov M M, Heinz T F, Marie X, Amand T, Urbaszek B 2018 Rev. Mod. Phys. 90 021001 Google Scholar
[3]	Zhang X, Qiao X F, Shi W, Wu J B, Jiang D S, Tan P H 2015 Chem. Soc. Rev. 44 2757 Google Scholar
[4]	Song Q J, Tan Q H, Zhang X, Wu J B, Sheng B W, Wan Y, Wang X Q, Dai L, Tan P H 2016 Phys. Rev. B 93 115409 Google Scholar
[5]	Leng Y C, Lin M L, Zhou Y, Wu J B, Meng D, Cong X, Li H, Tan P H 2021 Nanoscale 13 9732 Google Scholar
[6]	Kim K, Lee J U, Nam D, Cheong H 2016 ACS Nano 10 8113 Google Scholar
[7]	Tan Q H, Sun Y J, Liu X L, Zhao Y, Xiong Q, Tan P H, Zhang J 2017 2D Mater. 4 031007 Google Scholar
[8]	Kim S, Kim K, Lee J, Cheong H 2017 2D Mater. 4 045002
[9]	Tan P H 2019 Raman Spectroscopy of Two-Dimensional Materials (Singapore: Springer) pp203–227
[10]	张琼予, 崔旭伟, 董文龙, JARAPANYACHEEP Rapisa, 刘璐琪 2025 光散射学报 37 188 Google Scholar Zhang Q Y, Cui X W, Dong W L, Jarapanyacheep R, Liu L Q 2025 Chin. J. Light Scatt. 37 188 Google Scholar
[11]	蒋杰, 李聪慧, 姚森浩, 申珅, 冉娜, 张洁 2024 光散射学报 36 305 Google Scholar Jiang J, Li C H, Yao S H, Shen S, Ran N, Zhang J 2024 Chin. J. Light Scatt. 36 305 Google Scholar
[12]	Liu Y, Hu X, Wang T, Liu D 2019 ACS Nano 13 14416 Google Scholar
[13]	Shi H, Yan R, Bertolazzi S, Brivio J, Gao B, Kis A, Jena D, Xing H G, Huang L 2013 ACS Nano 7 1072 Google Scholar
[14]	Mei R, Zhong Y G, Xie J L, Wu J B, Du W N, Zhang X H, Liu X F, Lin M L, Tan P H 2025 Laser Photonics Rev. e00821 Google Scholar
[15]	Jiang Y, Chen S, Zheng W, Zheng B, Pan A 2021 Light Sci. Appl. 10 72 Google Scholar
[16]	Li H, Wu J B, Ran F, Lin M L, Liu X L, Zhao Y, Lu X, Xiong Q, Zhang J, Huang W, Zhang H, Tan P H 2017 ACS Nano 11 11714 Google Scholar
[17]	Huang Y, Sutter E, Shi N N, Zheng J, Yang T, Englund D, Gao H J, Sutter P 2015 ACS Nano 9 10612 Google Scholar
[18]	Castellanos-Gomez A, Buscema M, Molenaar R, Singh V, Janssen L, Van Der Zant H S, Steele G A 2014 2D Mater. 1 011002 Google Scholar
[19]	Zhang X, Han W P, Wu J B, Milana S, Lu Y, Li Q Q, Ferrari A C, Tan P H 2013 Phys. Rev. B 87 115413 Google Scholar
[20]	Tan P H, Han W P, Zhao W J, Wu Z H, Chang K, Wang H, Wang Y F, Bonini N, Marzari N, Pugno N, Savini G, Lombardo A, Ferrari A C 2012 Nat. Mater. 11 294 Google Scholar
[21]	Wu J B, Zhang X, Ijäs M, Han W P, Qiao X F, Li X L, Jiang D S, Ferrari A C, Tan P H 2014 Nat. Commun. 5 5309 Google Scholar
[22]	Liang L, Zhang J, Sumpter B G, Tan Q H, Tan P H, Meunier V 2017 ACS Nano 11 11777 Google Scholar
[23]	Pierucci D, Henck H, Avila J, Balan A, Naylor C H, Patriarche G, Dappe Y J, Silly M G, Sirotti F, Johnson A T C, Asensio M C, Ouerghi A 2016 Nano Lett. 16 4054 Google Scholar
[24]	Bieniek M, Szulakowska L, Hawrylak P 2020 Phys. Rev. B 101 125423 Google Scholar
[25]	Robert C, Han B, Kapuscinski P, Delhomme A, Faugeras C, Amand T, Molas M R, Bartos M, Watanabe K, Taniguchi T, Urbaszek B, Potemski M, Marie X 2020 Nat. Commun. 11 4037 Google Scholar
[26]	Carvalho B R, Malard L M, Alves J M, Fantini C, Pimenta M A 2015 Phys. Rev. Lett. 114 136403 Google Scholar
[27]	Niu Y, Gonzalez-Abad S, Frisenda R, Marauhn P, Drüppel M, Gant P, Schmidt R, Taghavi N S, Barcons D, Molina-Mendoza A J, De Vasconcellos S M, Bratschitsch R, Perez De Lara D, Rohlfing M, Castellanos-Gomez A 2018 Nanomaterials 8 725 Google Scholar
[28]	Zhou K G, Withers F, Cao Y, Hu S, Yu G, Casiraghi C 2014 ACS Nano 8 9914 Google Scholar
[29]	Tan Q H, Zhang X, Luo X D, Zhang J, Tan P H 2017 J. Semicond. 38 031006 Google Scholar

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Room-temperature Raman detection of all Davydov components of ${\mathrm{A}}_1' $ mode in transition metal dichalcogenides

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Corresponding author: TAN Pingheng, phtan@semi.ac.cn

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Room-temperature Raman detection of all Davydov components of ${\mathrm{A}}_1' $ mode in transition metal dichalcogenides

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Corresponding author: TAN Pingheng, phtan@semi.ac.cn

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