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Scanning electron micrographs of the vertical metallic nanowires viewed from side (a) and top (b). (c) Unit cell of the rectangular array centered on the plasmon nanocavity. The geometry of the array is specified by the pitch, radius, and height of the nanowire array. Optical excitation of the cavity with normal incidence light polarized in the transverse magnetic mode. (d) Simulations of the electric field amplitude in the resonator seen from front, side, and top. (e) Nano-focusing in the plasmon cavity mode. Tangential power flow in the vertical symmetry planes of the cavity highlights the electromagnetic energy channeling into the inter-wire region from the top and the sides of the cavity.
(a) Simulations of normal incidence reflectance for a gold nanocavity 1150 nm long, 50 nm wide, showing resonances of order 5, 6, and 7 (from left to right) as reflectivity minima. (b) Electric field amplitude simulation of the plasmon mode in the center of the cavity plotted as a function of position and excitation wavelength. Across the continuum of resonant modes, only the ones that have a large overlap with the incident photon modes are optically excited.
Simulations of the normal incidence reflected power for gold, silver, and aluminum as a function of wavelength and nanowire height (color plot). Multiple resonances can be excited below the plasmon cutoff frequency. Experimental reflectivity for flat metallic films and nanowire arrays of increasing height, for gold, silver, and aluminum is plotted alongside representative scanning electron micrographs cross sections. In all plots, the reflectivity scale is 0 to 1.
Simulated averaged visible reflectivity (400–800 nm) of an array of metallic nanowires as a function of the nanowire height for gold (red), silver (blue), and aluminum (green). The color coded dashed lines represent the average reflectivity for the flat metallic films, and the symbols are experimental measurements. A significant portion of the incident radiation is absorbed in plasmon resonant modes.
Experimental reflectance data highlighting transition from the nano-wire structures to sharp tapered grooves with increasing deposition time from light to darker color for the metallic layer (gold, silver, and aluminum). Lower reflectivity curves correspond to increased deposition time.
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