Fig. 4: Triangular hole metasurface.
From: Ultrathin 3R-MoS2 metasurfaces with atomically precise edges for efficient nonlinear nanophotonics
a High-resolution scanning electron microscopy (SEM) image of the h = 24.5 ± 1.5 nm thick metasurface. The scale bar is 1 μm. Inset is a close-up SEM image of the metasurface. The scale bar is 400 nm. b(i) High-resolution transmission electron microscopy image of a vertex of one of the triangular holes in a 3R-MoS2 metasurface with a beam direction along the [0001] zone axis. The scale bar is 5 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. 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. The orientation between the {1100} family of spots in the FFT and the edges of the triangle in the image confirm the zigzag nature of the etched edges. (ii) High-resolution scanning transmission electron microscopy image of a representative triangular hole edge. The overlays show possible zigzag and armchair directions, confirming the edge is aligned with the zigzag direction. The scale bar is 2 nm. c Experimental back focal plane reflection spectroscopy of the metasurface for transverse electric (TE) and transverse magnetic (TM) modes with 2 close-ups. TLR triangular lattice resonance, qBIC quasi-bound-state-in-the-continuum. d Numerically calculated reflection spectra at different angles of reflection for TE and TM modes with similar close-ups using following parameters: atri = 375 nm, pitch size Λ = 500 nm, h = 20 nm.
