Flexibly tunable surface plasmon resonance by strong mode coupling using a random metal nanohemisphere on mirror

• Published in: Nanophotonics (Berlin, Germany) Vol. 9; no. 10; pp. 3409 - 3418
• Main Authors: Okamoto, Koichi, Okura, Kota, Wang, Pangpang, Ryuzaki, Sou, Tamada, Kaoru
• Format: Journal Article
• Language: English
• Published: Berlin De Gruyter 01.09.2020; Walter de Gruyter GmbH
• Subjects: Coupled modes; Coupling; Efficiency; Glass substrates; Light; mode coupling; Nanofabrication; nanohemisphere on mirror; Nanoparticles; Nanospheres; Optical properties; Optimization; plasmonics; Q factors; strong coupling; Substrates; surface plasmon; Surface plasmon resonance; Thickness
• ISSN: 2192-8606; 2192-8614
• DOI: 10.1515/nanoph-2020-0118

We propose a unique random metal nanohemisphere on mirror (NHoM) structure to tune the surface plasmon (SP) resonance in a flexible manner. The SP resonance peak was split into two peaks owing to the strong coupling between the SP mode in the metal nanohemisphere and the mirror image mode generated in the metal substrate. This phenomenon is based on the fact that the strong coupling and the induced electromagnetic effects are similar to those pertaining to the Rabi splitting, Fano resonance, and electromagnetically induced transparency, thus providing quantum effect analogies. These phenomena have recently attracted increased attention and have been studied with nanocavities fabricated with top-down nanotechnologies. Compared with previous reports, NHoM structures can be fabricated in a much easier manner and are tunable in rather wider wavelength regions without nanofabrication technologies. The SP resonance peaks were enhanced, sharpened dramatically, and tuned flexibly, based on the optimization of the thickness of the spacer layer between the metal hemisphere and metal substrate. Experimental results were reproduced and were explained based on finite difference time domain (FDTD) simulations. These phenomena have never been observed previously on similar nanosphere on mirror (NSoM) because nanohemispherical structures were required. The NHoM nanocavity structure has a quality factor >200 that is surprisingly high for the localized SP mode of nanoparticles. Flexible tuning of the SP resonance with the use of NHoM is envisaged to lead to the development of new applications and technologies in the field of plasmonics and nanophotonics.