Abstract
We propose a novel mirror-image nanoepsilon (MINE) structure to achieve highly localized and enhanced near field at its gap and systematically investigate its plasmonic behaviors. The MINE can be regarded as a combination of two fundamental plasmonic nanostructures: a nanorod dimer and nanoring. By adapting a nanoring surrounding a nanorod dimer structure, the nanorod is regarded as a bridge pulling the charges from the nanoring to the nanorod, which induces stronger plasmon coupling in the gap to boost local near-field enhancement. Two resonance peaks are identified as the symmetric and anti-symmetric modes according to the symmetries of the charge distributions on the ring and rod dimer in the MINE. The symmetric mode in the MINE structure is preferred because its charge distribution leads to stronger near-field enhancement with a concentrated distribution around the gap. In addition, we investigate the influence of geometry on the optical properties of MINE structures by performing experiments and simulations. These results indicate that the MINE possesses highly tunable optical properties and that significant near-field enhancement at the gap region and rod tips can be realized by the gap and lightning-rod effects. The results improve understanding of such complex systems, and it is expected to guide and facilitate the design of optimum MINE structures for various plasmonic applications.
Highlights
Metallic nanostructures with localized surface plasmon resonance (LSPR) provide a method for manipulating light at the nanoscale beyond the optical diffraction limit [1, 2]
Combining the features of a nanoring and a nanorod dimer, we propose a novel mirror-image nanoepsilon (MINE), which is equal to two mirrored nanoscale ε-shaped structures, to boost the local near-field enhancement for various applications that require highly localized and enhanced field
We investigate the influence of geometry on the optical properties of MINE structure for obtaining a highly localized and enhanced near field
Summary
Metallic nanostructures with localized surface plasmon resonance (LSPR) provide a method for manipulating light at the nanoscale beyond the optical diffraction limit [1, 2]. The field intensity can be dramatically enhanced in the gap region of the metallic dimer due to the near-field coupling effect when two nanostructures are sufficiently close to each other. The optical field can be improved by several orders of magnitude by modifying the gap distance or the rod width of a nanorod dimer. Such highly localized and enhanced near fields in the dimer system have been utilized to miniaturize the trapping spot size and simultaneously promote the induced optical forces for optical tweezers. Zhang et al have demonstrated that 10nm metal nanoparticles can be trapped and sensed with the nanorod dimer [35]
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