Metallic tips for efficient plasmon nanofocusing and advanced optical nano-imaging

Abstract

Plasmon nanofocusing, a phenomenon where plasmons propagate on a tapered metallic structure with compressing its energy into a nanometric volume of the apex to generate localized electric field, holds a great promise for near-field optical imaging techniques due to its background-free nature. Because it does not require to illuminate the tip apex with an incident laser, one can efficiently eliminate scattering background noise by the incident laser, which has been an issue in conventional near-field optical microscopies. To apply plasmon nanofocusing for near-field optical imaging, a tapered metallic tip plays an important role as a base material for plasmon propagation. It is therefore essential to establish an efficient and practical methods of the metallic tip fabrication for plasmon-nanofocusing-based optical imaging techniques. In this study, we propose an optimized tip fabrication for efficient plasmon nanofocusing, which achieved 100% reproducibility in plasmon nanofocusing. Through numerical analysis, we have optimized the tip structure, such as types of material, metal thickness, plasmon coupler structure, etc. Also, the fabrication conditions were well-optimized to obtain smooth metal surface down to 0.5 nm roughness to reduce energy loss of plasmon propagation. Through thorough optimizations, we observed plasmon nanofocusing with 100% reproducibility in more than 20 fabricated metallic tips. Such efficient, reliable and practical tip fabrication opens the doors for many potential scientists working in related fields.