Acta Physica Sinica, Volume. 69, Issue 18, 184210-1(2020)

Second harmonic generation of two-dimensional layered materials: characterization, signal modulation and enhancement

Zhou-Xiao-Song Zeng1... Xiao Wang1,* and An-Lian Pan2,* |Show fewer author(s)
Author Affiliations
  • 1Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronic Science, Hunan University, Changsha 410082, China
  • 2Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Materials Science and Engineering, Hunan University, Changsha 410082, China
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    Figures & Tables(10)
    (a) Side view (left) and top view (right) of MoS2 atomic structure. The highlighted armchair direction and zigzag direction correspond to the top view. (b) Mechanical exfoliated MoS2 with different layers[16]. (c) 2H phase MoS2 layers show diminishing the oscillation in SHG signal[16]. (d) Optical image of artificial folded MoS2(left) and its corresponding SHG image(right)[31]. (e) Crystal structure of 3R phase MoS2 and corresponding SH dipole[32]. (f) 3R phase MoS2 layers show quadratic enhanced SHG with the increase of layers[32].
    CVD grown TMDCs with highly efficient SHG: (a) Optical image (left) and zoom in AFM image (right) of spiral WS2 flake[39]; (b) layer dependent SHG of spiral WS2 flake[39]; (c) schematic illustration of pyramid-like WS2 structure[41]; (d) pyramid-like WS2 displays high intensity of residual edge SHG signal[41].
    Polarization properties of SHG in TMDCs: (a) SHG polarization in monolayer MoS2 shows six fold rotation symmetry[16]; (b) top view of MoS2 crystallographic orientation, where x represents armchair direction, y represents zigzag direction and θ is the angle between input laser and armchair direction [16]; SHG polarization in (c) WS2/MoS2 laterally epitaxial heterostructure[44] and (d) WSe2/WS2 AA, AB vertical heterostructure[45], where the insets shows correspongding SHG mapping; (e) superposition of SHG polarization by artificial stacks of two different 2D materials[46]; (f)−(h) demonstration of distinguishing of different grain boundary in monolayer MoS2 thin film be SHG polarization[47].
    Exciton resonance properties of SHG in TMDCs: (a) Schematic illustration of SHG when two incident photons are resonant with 2p state of A exciton[50]; (b) excitation wavelength dependent SHG of monolayer WSe2 at T = 4 K[50]; (c) second order nonlinear susceptibility and absorption served as the function of pump laser energy in monolayer (blue) and trilayer (green) MoS2[16]; (d), (e) illustration of SHG enhancement in spiral WS2 flake when the excitation energy slightly above bandgap by comparison of reflective spectrum with SHG spectrum[51]; (f) SHG spectra (dotted traces) of monolayer alloys and corresponding room-temperature PL spectra (solid traces)[52]; (g), (h) CVD grown monolayer MoS2 flakes show edge enhanced SHG[47].
    SHG valley selection rules: (a) Circular polarization-resolved SHG spectra showing the generation of counter-circular SHG in monolayer WSe2[59]; (b) interband valley optical selection rules for SHG in 2D TMDCs[59].
    Electric field modulated SHG: (a) Schematic illustration of bilayer MoS2 microcapacitor device[67]; (b) bilayer MoS2 SHG intensity as the function of applied voltage and SHG emission energy[67]; (c) reversible SHG induced by back gate in bilayer WSe2[66]; (d) optical image of monolayer WSe2 transistor[59]; (e) exciton resonant monolayer WSe2 SHG spectra at selected gate voltage[59]; (f) monolayer WSe2 SHG intensity as the function of applied gate voltage and SHG emission energy[59].
    Strain modulated SHG: (a) MoSe2 SHG polarization changed by uniaxial tensile strain[26]; (b) uniaxial strain map of MoS2 monolayer flake[75]; (c) schematic illustration (up) and SHG mapping (down) of TiO2/MoS2 structure[77].
    Metasurfaces modulated SHG: (a) Schematic illustration of a MoS2-gold phased array antenna steering SHG emission[81]; (b) polar plot of the calculated (line) and measured (points) SH pattern along the intensity maximum when phase delay δx = δy = 0[81]; (c) the SEM image of the fabricated gold metasurface with rectangular nanoholes of different orientation[82]; (d) the experimental results of SHG focusing by using the hybrid metasurfaces[82]; (e) schematic representations of steering second-harmonic waves on RCP pumping with monolayer WS2[79]; (f) evolution of the light field for the case shown in (c), “0” and “1” label the intensity order[79].
    SHG enhancement by plasmonics: (a) Nano cavity strongly confines incident light field (up), and SHG enhancement by Ag nanoparticle in monolayer WS2 (down)[92]; (b) compare of SHG signal in different plasmonic array/semiconductor, where points 1, 2, 3 represent the area of nanorod, nanorod/bilayer WSe2, and bilayer WSe2, respectively[93]; (c) SHG enhancement factor over 400 in monolayer WS2 reached by Ag nanogroove grating[94]; (d) SHG enhancement over 3 orders in monolayer WSe2 by plasmonic structure on PDMS[95].
    SHG enhancement by micro cavity and photonic crystal: (a) Enhancement of SHG from monolayer MoS2 in a doubly resonant on-chip optical cavity[100]; (b) enhancement of SHG by silicon waveguide[105]; (c) CW excitation of SHG from GaSe/photonic crystal[106].
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    Zhou-Xiao-Song Zeng, Xiao Wang, An-Lian Pan. Second harmonic generation of two-dimensional layered materials: characterization, signal modulation and enhancement[J]. Acta Physica Sinica, 2020, 69(18): 184210-1

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    Paper Information

    Received: Mar. 27, 2020

    Accepted: --

    Published Online: Jan. 5, 2021

    The Author Email: Pan An-Lian (anlian.pan@hnu.edu.cn)

    DOI:10.7498/aps.69.20200452

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