[19p-PA6-1~28] 3.12 Nanoscale optical science and near-field optics

▲ [19p-PA6-24] Substantial plasmonic field enhancement with tunable broadband resonances from a faceted nanoparticle on a metallic mirror nanostructure

〇(P)Vasanthan Devaraj¹, Jong-Min Lee¹, Samir Adhikari², Won-Geun Kim¹, Minjun Kim², Yong-Cheol Kang³, Donghan Lee², Jin-Woo Oh¹ (1.Pusan Natl. Univ, 2.Chungnam Natl. Univ, 3.Pukyong Natl. Univ)

Keywords:Plasmonics, Surface charge distribution, Near-field enhancement

In metallic nanostructures, an interesting phenomenon originates from plasmonic nanogap or hot-spot, where the coupled plasmonic modes confine at the nanoscale and result in an extremely high near-field enhancement. This enhanced local fields will act as a powerful building block for plasmonic nanostructures for variety of applications. In this work, we introduce a nanoparticle on a metallic mirror (NPoM) structure with flat bottom nanoparticle (NP) structural modification, so called as facet (f). A detailed three-dimensional FDTD simulation studies were carried out where we find a variety of complex transverse cavity modes originate due to NP faceting. It is found that the dominant cavity mode resonance wavelength can be tuned widely from 600 nm to 1.5 µm, as a function of NP facet width. More importantly, despite being tuned to such broadband range, only a minimal decrease in near-field enhancement were noted. Additionally, we checked simulations for different NP diameter sizes and realized it is possible to achieve the near field enhancement in orders of ~ 10^9 even in case of smaller NPs with 50 nm diameter due to NP faceting effect. Alongside with cross-section electric field amplitude profiles, we used three-dimensional surface charge mappings, which identified the origin of plasmonic modes arising from either NP or cavity. From our surface charge simulations, we found that the number of radial modes was dependent upon the combination of NP faceting width and diameter. These optical properties will see significant advantages in surface-enhanced spectroscopy, colour sensor applications, and device fabrication perspective. By exploring above such interesting and complex sub-wavelength optical properties of the plasmonic nanostructures, a variety of new applications can be found in fields of non-linear optics, photonics, sensors, device engineering, broadband tunable devices, surface enhanced spectroscopy and non-linear plasmonics.