M.S. Lapteva1, A.V. Gorbatova2, P.Yu. Avdeev3, D.A. Abdullaev4, A.I. Kartsev5, E.A. Bulavintseva6, A.A. Klimov7, A.M. Buryakov8

1–3, 5–8 MIREA – Russian Technological University (Moscow, Russia)
4 Institute of Nanotechnology of Microelectronics of the Russian Academy of Sciences (Moscow, Russia)
5 RUDN University (Moscow, Russia)
7 Kotelnikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences ((Moscow, Russia)
1 lapteva@mirea.ru, 2 gorbatova@mirea.ru, 3 avdeev_p@mirea.ru, 4 abdullaev.d@inme-ras.ru, 5 karec1@gmail.com, 6 bulavinceva@mirea.ru, 7 klimov@mirea.ru, 8 buryakov@mirea.ru

Problem Statement: there is a need to create spintronic terahertz radiation sources that go beyond traditional ferromagnet/heavy metal heterostructures. Two-dimensional transition metal dichalcogenides (TMDs) are promising as an interface for spin-charge conversion, but integrating TMDs obtained by liquid-phase exfoliation into THz emitters remains a technologically and methodologically challenging task.

Objective: to fabricate and characterize spintronic THz emitters based on TMD/Co heterostructures obtained by liquid-phase exfoliation, assessing the THz signal amplitude, and evaluate the role of interfacial spin-orbit conversion.

Results: spintronic THz emitters were fabricated based on heterostructures of three types of dichalcogenides (WS2, WSe2, MoSe2) synthesized by liquid-phase exfoliation. Morphological analysis (scanning electron microscopy, atomic force microscopy) revealed a high coverage density of TMD crystallites (60–80%) with a characteristic size of 5–10 μm and a height of 20–500 nm. Analysis of the phase characteristics of THz pulses shows that, with integral recording, the dominant generation mechanism is ultrafast laser-induced demagnetization of cobalt.

Practical Relevance: this work demonstrates the potential of liquid-phase exfoliation as a method for producing active layers of spintronic THz sources. Replacing expensive heavy metals with two-dimensional semiconductors reduces costs and improves the scalability of the technology.

1. Banks P.A., Kleist E.M., Ruggiero M.T. Investigating the Function and Design of Molecular Materials through Terahertz Vibrational Spectroscopy. Nat. Rev. Chem. 2023:7(7):480–495. https://doi.org/10.1038/s41570-023-00487-w.
2. Wu Y., Wang Y., Bao D., Deng X., Zhang S., Yu-chun L., Ke S., Liu J., Liu Y., Wang Z., Ham P., Hanna A., Pan J., Hu X., Li Z., Zhou J., Wang C. Emerging Probing Perspective of Two-Dimensional Materials Physics: Terahertz Emission Spectroscopy. Light Sci. Appl. 2024:13(1):146. https://doi.org/10.1038/s41377-024-01486-2.
3. Seifert T.S., Cheng L., Wei Z., Kampfrath T., Qi J. Spintronic Sources of Ultrashort Terahertz Electromagnetic Pulses. Appl. Phys. Lett. 2022:120(18). https://doi.org/10.1063/5.0080357.
4. Hawecker J., Rongione E., Markou A., Krishnia S., Godel F., Collin S., Lebrun R., Tignon J., Mangeney J., Boulier T., George J.-M., Felser C., Jaffrès H., Dhillon S. Spintronic THz Emitters Based on Transition Metals and Semi-Metals/Pt Multilayers. Appl. Phys. Lett. 2022:120(12). https://doi.org/10.1063/5.0079955.
5. Papaioannou E.T., Beigang R. THz Spintronic Emitters: A Review on Achievements and Future Challenges. Nanophotonics. 2021:10(4):1243–1257. https://doi.org/10.1515/nanoph-2020-0563.
6. Pimenov N., Kartsev A., Lebedeva E., Mishina E. Fingerprint Raman Spectroscopy for Two-Dimensional MoS 2 x Se 2(1–x) Alloys. J. Phys. Condens. Matter. 2024:36(23):235303. https://doi.org/10.1088/1361-648X/ad2e26.
7. Kormányos A., Zólyomi V., Drummond N.D., Burkard G. Spin-Orbit Coupling, Quantum Dots, and Qubits in Monolayer Transition Metal Dichalcogenides. Phys. Rev. X. 2014:4(1):011034. https://doi.org/10.1103/PhysRevX.4.011034.
8. Wang G., Robert C., Suslu A., Chen B., Yang S., Alamdari S., Gerber I.C., Amand T., Marie X., Tongay S., Urbaszek B. Spin-Orbit Engineering in Transition Metal Dichalcogenide Alloy Monolayers. Nat. Commun. 2015:6(1):10110. https://doi.org/10.1038/ncomms10110.
9. Docherty C.J., Parkinson P., Joyce H.J., Chiu M.-H., Chen C.-H., Lee M.-Y., Li L.-J., Herz L.M., Johnston M.B. Ultrafast Transient Terahertz Conductivity of Monolayer MoS 2 and WSe 2 Grown by Chemical Vapor Deposition. ACS Nano. 2014:8(11):11147–11153. https://doi.org/10.1021/nn5034746.
10. Buryakov A.M., Gorbatova A.V., Avdeev P.Y., Lebedeva E.D., Gusev N.S., Karashtin E.A., Pashen’kin I.Y., Sapozhnikov M.V., Mishina E.D. Hybrid Co/2D-WSe2-Based THz Spintronic Emitter with Tunable Polarization. Appl. Phys. Lett. 2025:127(5). https://doi.org/10.1063/5.0274793.
11. Roy A., Ghosh R., Rai A., Sanne A., Kim K., Movva H.C.P., Dey R., Pramanik T., Chowdhury S., Tutuc E., Banerjee S.K. Intra-Domain Periodic Defects in Monolayer MoS2. Appl. Phys. Lett. 2017:110(20). https://doi.org/10.1063/1.4983789.
12. Cheng L., Wang X., Yang W., Chai J., Yang M., Chen M., Wu Y., Chen X., Chi D., Goh K.E.J., Zhu J.-X., Sun H., Wang S., Song J.C.W., Battiato M., Yang H., Chia E.E.M. Far Out-of-Equilibrium Spin Populations Trigger Giant Spin Injection into Atomically Thin MoS2. Nat. Phys. 2019:15(4):347–351. https://doi.org/10.1038/s41567-018-0406-3.
13. Kłopotowski Ł., Backes C., Mitioglu A.A., Vega-Mayoral V., Hanlon D., Coleman J.N., Ivanov V.Y., Maude D.K., Plochocka P. Revealing the Nature of Excitons in Liquid Exfoliated Monolayer Tungsten Disulphide. Nanotechnology. 2016:27(42):425701. https://doi.org/10.1088/0957-4484/27/42/425701.
14. Li Z., Rashvand F., Bretscher H., Szydłowska B.M., Xiao J., Backes C., Rao A. Understanding the Photoluminescence Quenching of Liquid Exfoliated WS 2 Monolayers. J. Phys. Chem. C. 2022:126(51):21681–21688. https://doi.org/10.1021/acs.jpcc.2c05284.
15. Chavalekvirat P., Hirunpinyopas W., Deshsorn K., Jitapunkul K., Iamprasertkun P. Liquid Phase Exfoliation of 2D Materials and Its Electrochemical Applications in the Data-Driven Future. Precis. Chem. 2024:2(7):300–329. https://doi.org/10.1021/prechem.3c00119.
16. Telkhozhayeva M., Teblum E., Konar R., Girshevitz O., Perelshtein I., Aviv H., Tischler Y.R., Nessim G.D. Higher Ultrasonic Frequency Liquid Phase Exfoliation Leads to Larger and Monolayer to Few-Layer Flakes of 2D Layered Materials. Langmuir. 2021:37(15):4504–4514. https://doi.org/10.1021/acs.langmuir.0c03668.
17. Tao H., Zhang Y., Gao Y., Sun Z., Yan C., Texter J. Scalable Exfoliation and Dispersion of Two-Dimensional Materials – an Update. Phys. Chem. Chem. Phys. 2017:19(2):921–960. https://doi.org/10.1039/C6CP06813H.
18. Huo C., Yan Z., Song X., Zeng H. 2D Materials via Liquid Exfoliation: A Review on Fabrication and Applications. Sci. Bull. 2015:60(23): 1994–2008. https://doi.org/10.1007/s11434-015-0936-3.
19. Backes C., Higgins T.M., Kelly A., Boland C., Harvey A., Hanlon D., Coleman J.N. Guidelines for Exfoliation, Characterization and Processing of Layered Materials Produced by Liquid Exfoliation. Chem. Mater. 2017:29(1):243–255. https://doi.org/10.1021/ acs.chemmater.6b03335.
20. Jung G.-H., Yoo S., Park Q.-H. Measuring the Optical Permittivity of Two-Dimensional Materials without a Priori Knowledge of Electro­nic Transitions. Nanophotonics. 2019:8(2):263–270. https://doi.org/10.1515/nanoph-2018-0120.
21. Hsu C., Frisenda R., Schmidt R., Arora A., de Vasconcellos S.M., Bratschitsch R., van der Zant H.S.J., Castellanos-Gomez A. Thickness‐Dependent Refractive Index of 1L, 2L, and 3L MoS 2, MoSe 2, WS 2, and WSe 2. Adv. Opt. Mater. 2019:7(13). https://doi.org/ 10.1002/adom.201900239.
22. Berger A.J., Amamou W., White S.P., Adur R., Pu Y., Kawakami R.K., Hammel P.C. Magnetization Dynamics of Cobalt Grown on Graphene. J. Appl. Phys. 2014:115(17). https://doi.org/10.1063/1.4864742.
23. Lu C.-I., Huang C.-H., Ou Yang K.-H., Simbulan K.B., Li K.-S., Li F., Qi J., Jugovac M., Cojocariu I., Feyer V., Tusche C., Lin M.-T., Chuang T.-H., Lan Y.-W., Wei D.-H. Spontaneously Induced Magnetic Anisotropy in an Ultrathin Co/MoS 2 Heterojunction. Nanoscale Horizons. 2020:5(7):1058–1064. https://doi.org/10.1039/D0NH00108B.
24. Cheng L., Wang X., Yang W., Chai J., Yang M., Chen M., Wu Y., Chen X., Chi D., Goh K.E.J., Zhu J.X. Far out-of-equilibrium spin populations trigger giant spin injection into atomically thin MoS2. Nat. Phys. 2019:15(4):347 -351. https://doi.org/10.1038/s41567-018-0406-3.
25. Buryakov A., Gorbatova A., Avdeev P., Bezvikonnyi N., Abdulaev D., Klimov A., Ovcharenko S., Mishina E. Controlled Spintronic Emitter of THz Radiation on an Atomically Thin WS2/Silicon Substrate. Metals. 2022:12(10):1676. https://doi.org/10.3390/met12101676.