「Deep-UV optical studies of two-dimensional materials」
Prof. Hsiang-Lin Liu氏

日本物理学会北海道支部講演会

講演題目：　Deep-UV optical studies of two-dimensional materials
講　師　：　Prof. Hsiang-Lin Liu氏
　　　　　　Department of Physics, National Taiwan Normal University
日時: 2023年11月6日(月)　17:00-18:00
場　所　：　北海道大学理学部２号館　2-211
要　旨　：
We present the deep-UV optical studies of two-dimensional materials, including graphene and transition metal dichalcogenides. Our experimental techniques are deep-UV Raman and spectroscopic ellipsometry. First, the Raman intensities from the second-order phonon modes of monolayer graphene and monolayer MoS2 and WS2 are revealed to be decreased or enhanced anomalously by the deep-UV excitation wavelength [1-3]. We demonstrate theoretically that such resonant behavior correlates with the absorption properties and electron-phonon interactions in these materials. Second, the optical absorption spectra of monolayer and bilayer graphene exhibit two broad bands over the UV spectral region. Based on the first-principles calculations, we assign the observed two absorptions to an excitonic transition at the saddle point (M) in the band structures and collective excitations of the surface plasmons [4,5]. These results advance our understanding of the double resonance Raman scattering process, quasiparticle band structures, and collective excitations of two-dimensional materials.

[1] H. L. Liu*, S. Siregar, E. H. Hasdeo, Y. Kumamoto, C. C. Shen, C. C. Cheng, L. J. Li, R. Saito, and S. Kawata, “Deep-ultraviolet Raman scattering studies of monolayer graphene thin films”, Carbon 81, 807-813 (2015).
[2] H. L. Liu*, H. Guo, T. Yang, Z. Zhang, Y. Kumamoto, C. C. Shen, Y. T. Hsu, L. J. Li, R. Saito, and S. Kawata, “Anomalous lattice vibrations of monolayer MoS2 probed by ultraviolet Raman scattering”, Physical Chemistry Chemical Physics 17, 14561-14568 (2015).
[3] H. L. Liu*, T. Yang*, Y. Tatsumi, Y. Zhang, B. Dong, H. Guo, Z. Zhang, Y. Kumamoto, M. Y. Li, L. J. Li, R. Saito, and S. Kawata,“Deep-ultraviolet Raman scattering spectroscopy of monolayer WS2”, Scientific Reports 8, 11398-1~10 (2018).
[4] D. P. Gulo, N. T. Hung, T. J. Yang, G. J. Shu, R. Saito, and H. L. Liu*, “Exploring unusual temperature-dependent optical properties of graphite single crystals by spectroscopic ellipsometry”, Carbon 197, 485-493 (2022).
[5] H. L. Liu*, B. D. Annawati, N. T. Hung, D. P. Gulo, P. Solis-Fernandez, K. Kawahara, H. Ago, and R. Saito, “Interference of excitons and surface plasmons in the optical absorption spectra of monolayer and bilayer graphene”, Physical Review B 107, 165421-1~10 (2023).

世話人：　柳澤達也
（tatsuya@cris.hokudai.ac.jp)
北海道大学大学院理学研究院

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