Fig. 3: Circular hole metasurface.
From: Ultrathin 3R-MoS2 metasurfaces with atomically precise edges for efficient nonlinear nanophotonics
a Scanning electron microscopy (SEM) image of the circular hole 3R-MoS2 metasurface with h = 27 ± 1 nm. The scale bar is 1 μm. The inset shows a zoomed-in image of the metasurface. The scale bar is 400 nm. b High-resolution transmission electron microscopy image of one of the circular holes in a 3R-MoS2 metasurface with a beam direction along the [0001] zone axis. The scale bar is 10 nm. The inset shows the fast Fourier transform (FFT) of the image that exhibits distinct spatial frequency spots corresponding to the crystalline structure of the 3R-MoS2 and diffuse rings corresponding primarily to the amorphous SiN membrane support. The scale bar is 5 nm−1. The red and green circles identify the FFT spots that correspond to the 3R-MoS2 {1100} and {1120} families of crystallographic planes, respectively. c Experimental back focal plane reflection spectroscopy of the metasurface for transverse electric (TE) and transverse magnetic (TM) modes with 2 close-ups. The `SHG lens' indicates the effective numerical aperture of the lens during second harmonic generation experiments in air. CLR circular lattice resonance, BIC bound-state-in-the-continuum. Extracted parameters are Dhole = 278 ± 8 nm, Λx = 493 ± 7 nm, and Λy = 488 ± 8 nm. d Numerically calculated reflection spectra at different angles of reflection for TE and TM modes with similar close-ups. The parameters of the metasurface used in the calculation are: pitch Λ = 500 nm, D = 262.5 nm, h = 23 nm.
