This work thoroughly investigates binary nanowire gratings with nanogap spacing. A binary plasmonic grating is a periodic nanostructure for which each period has two different widths. The study has determined that plasmonic gratings with two different widths in each period give rise to optical enhancement that is 2.1 times stronger than that of standard plasmonic grating structures. A map of varying width ratios has been created to illustrate the key geometric characteristic for enhancement optimization. The structure under investigation was a gold structure with a constant height of 15 nm and a nanogap of 5 nm. The period size of the structure depends on the two nanowire widths in each grating period. The optical enhancement (E/E0)2 of the geometry was investigated using a finite element method (FEM) simulation for various wavelengths. The results show a strong correlation between the plasmon wavelength and the periodicity of the gratings. Additionally, the plasmonic charge distributions have been calculated for various periods and geometries. Various resonant modes exist for the charge distribution, significantly affecting the enhancement depending on the nanowire widths.
Ahmad A. Darweesh, Stephen J. Bauman, Zachary T. Brawley, and Joseph B. Herzog, "Improved optical enhancement in binary plasmonic gratings with nanogap spacing," Proc. SPIE 9927, Nanoengineering: Fabrication, Properties, Optics, and Devices XIII, 99270Z (Presented at SPIE Nanoscience + Engineering: August 31, 2016; Published: 15 September 2016); https://doi.org/10.1117/12.2237197.
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