Plasmon Resonances in a Convex–Concave Silver Nanoshell

The two-dimensional problem of diffraction of a plane electromagnetic wave is considered as a TM-type on a cylindrical nanoshell (structure) of silver, the outer and inner contours of the cross section of which are symmetrical convex-concave curves. In the wavelength range \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$320\,{\text{nm}} < \lambda < 1500\,{\text{nm}}$$\end{document} (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda $$\end{document} is the wavelength), the spectra of the scattering cross section, scattering diagrams, and the structure of the near field for resonant wavelengths are calculated by a rigorous numerical method. The influence of the geometric dimensions of the structure, the angle of incidence of a plane wave, and the relative permittivity of the shell core on the scattering cross section and the scattering diagram is studied. It is shown that such shells exhibit pronounced multipole resonances, the effect of near field degeneration, and the possibility of shifting the dipole resonance to the region of λ ≈ 1500–1700 nm and a significant difference in resonant wavelengths between dipole and multipole resonances.