Surface plasmons excited from close-packed nanoring tube arrays produced by nanosphere lithography

Two-dimensional (2D) periodical close-packed nanoring tube arrays (RTAs) composed of metal and dielectric materials with unique surface plasmon properties have been investigated. A new fabrication route, which uses conventional semiconductor fabrication methods, has been developed to produce large-area highly ordered close-packed RTAs in a controllable and inexpensive way. Optical properties of this structure, as well as its replica, are investigated by both the finite-difference-time-domain (FDTD) algorithm and experiments. The simulation results show that both BW-SPP modes and coupled cavity modes at separate wavelengths are excited in RTAs, in accordance with experimental results. These modes are dependent on the geometry of RTAs. Ag RTAs with high absorption over the visible and near IR range has been experimentally demonstrated, which can be used in solar cells and as chemical/biological sensors with miniature size. The RTAs can also be employed as templates for producing other nanostructures by the nano-imprint methods, such as non-close-packed cylindrical column arrays that can be applied to surface-enhanced Raman scattering (SERS) substrates.