Photonics Research, Volume. 6, Issue 11, 991(2018)

Raman spectroscopy regulation in van der Waals crystals

Wei Zheng1,3, Yanming Zhu1, Fadi Li2, and Feng Huang1、*
Author Affiliations
  • 1State Key Laboratory of Optoelectronic Materials and Technologies, School of Materials, Sun Yat-sen University, Guangzhou 510275, China
  • 2Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China
  • 3e-mail: zhengw37@mail.sysu.edu.cn
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    Figures & Tables(5)
    Typical Raman spectra of MoS2 and WS2 scattering from in-plane (ei⊥c axis). (a) Typical Raman-scattering spectrum of MoS2 excited by a 633 nm laser, and a large number of LA(M)-related RS modes are excited. All recoded modes in MoS2 Raman spectroscopy are identified as 179 [A1g(M)+LA(M)], 383 [E2g1(Γ)], 409 [A1g(Γ)], 421 [B2g2+E1u2(Γ−A)], 454 [2LA(M)], 465 [A2u(Γ)], 529 [E1g(M)+LA(M)], 572 [2E1g(Γ)], 600 [E2g1(M)+LA(M)], 644 [A1g(M)+LA(M)], 767 (unknown), 785 (unknown), and 824 (unknown) cm−1 [14,16]. (b) Typical Raman-scattering spectrum of WS2 excited by a 532 nm laser, and the recoded modes are identified as LA(M) at 175 cm−1, E2g1(M)−LA(M) at 195 cm−1, A1g(M)−LA(M) at 233 cm−1, 2LA(M)−2E2g2(M) at 298 cm−1, E1g(M) at 323 cm−1, 2LA(M) at 351 cm−1, A1g(Γ) at 421 cm−1, E2g1(M)+LA(M) at 523 cm−1, A1g(M)+LA(M) at 585 cm−1, and 4LA(M) at 701 cm−1 [9].
    Normalized optical absorption coefficients of the cross section (ki∥a axis) in (a) MoS2 and (b) WS2 calculated via first principles, where ordinate θ is the angle between the incident light polarized vector ei and the c axis of the crystals. The absorption coefficients of the in-plane area (ki∥c axis) in (c) MoS2 and (d) WS2, where the ordinate φ represents the angle between the incident light ei and the c axis.
    Improved Raman spectra of (a) MoS2 and (b) WS2 scattering from out-of-plane polarization (ei∥c axis). Compared to Fig. 1, the RS modes here are fully suppressed and the high SNR of the OP mode is highlighted.
    The cross-sectional angle-dependent polarized (CAP) Raman spectra of (a) MoS2 and (b) WS2, where the ordinate θ is defined as the angle between the incident light polarization ei and the c axis, and the in-plane angle-dependent polarized (IAP) Raman spectra of (c) MoS2 and (d) WS2, where the ordinate φ is defined as the angle between the incident light polarization ei and the a axis.
    Raman intensities of OP and RS modes extracted from Figs. 4(a) and 4(b) via Lorentzian fitting. (a) and (b) display angle-dependent intensities of A1g OP modes in MoS2 and WS2, respectively, and reveal a similar changing rule in MoS2 and WS2. The red line gives the corresponding fitting results based on the Raman selection rule, i.e., Eq. (1). (c) and (d) show the angle-dependent intensities of resonant scattering modes in layered MoS2 and WS2, respectively. All modes appear with the same θ angle dependence: when θ=(n+1/2)π, the scattering intensity reaches the highest value; while θ=nπ, the value approximates to zero.
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    Wei Zheng, Yanming Zhu, Fadi Li, Feng Huang. Raman spectroscopy regulation in van der Waals crystals[J]. Photonics Research, 2018, 6(11): 991

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    Paper Information

    Category: Spectroscopy

    Received: Jun. 29, 2018

    Accepted: Aug. 31, 2018

    Published Online: Oct. 11, 2018

    The Author Email: Feng Huang (huangfeng@mail.sysu.edu.cn)

    DOI:10.1364/PRJ.6.000991

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