Acta Physica Sinica, Volume. 69, Issue 18, 184210-1(2020)
Fig. 1. (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].
Fig. 2. 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].
Fig. 3. 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
Fig. 4. 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
Fig. 6. 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].
Fig. 8. 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
Fig. 9. 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].
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Zhou-Xiao-Song Zeng, Xiao Wang, An-Lian Pan.
Received: Mar. 27, 2020
Accepted: --
Published Online: Jan. 5, 2021
The Author Email: Pan An-Lian (anlian.pan@hnu.edu.cn)