Proceedings Article | 9 September 2019
KEYWORDS: Metals, Plasmonics, Deep ultraviolet, Mirrors, Light emitting diodes, Nanolithography, Silver, Oscillators, Silica, Ultraviolet radiation
Plasmonics has been studied and used for various optoelectronic applications include efficient light-emitting diodes (LEDs) [1]. Next important challenge is to develop device applications and to extend into wide wavelength regions [2]. Here, I present the new nanostructures and methods to tune the plasmonic resonances for wide wavelength range including deep UV.
Recently, we observed unusual localized surface plasmon (LSP) resonance spectra that have a narrow bandwidth and high intensity by fabricating multilayered Ag nanoparticle sheet structures [3]. The peaks of the extinction spectra were clearly split into two peaks on metal substrates, while this phenomenon was not observed on a transparent substrate. This optical phenomenon should be due to the mode splitting effect by the strong coupling. The strong dipole oscillator located near the metal interface can interact with the mirror image of the dipole oscillator, which has the opposite phase. This presents a powerful and useful technique to tune the strong mode coupling effect without any lithographic structures.
Quite recently, we also found the similar peak splitting and sharpened of the LSP spectra for random metal nano-hemispheres, fabricated by thermal annealing of metal thin layers, on metal substrates through thin SiO2 spacer layer. We call such structure nano-hemispheres on mirror (NHoM). The LSP spectra of Ag NHoM became much larger and sharper, and also tunable in UV to visible wavelength region by the spacer thickness of the structure. In order to extend this technique into deep UV region, we fabricated NHoM structures by using aluminum which has the LSP resonance in ultra-deep UV regions. We obtained very strong and sharp resonance peak due to the mode splitting effect by the strong coupling at 156 nm by the by the electromagnetic simulations. As far as we know, this is the LSP spectrum which has the shortest peak wavelength in ultra-deep-UV region. The similar LSP spectra in deep UV region were obtained by experiments and found to be well tunable by the thickness of the SiO2 spacers.
I believe that our approaches using tunable plasmonics including Deep-UV region will bring high efficient plasmonic LEDs with practical use level and will develop future optic and photonic technologies for smart societies.
[1] K. Okamoto, I. Niki, A. Shvartser, Y. Narukawa, T. Mukai, A. Scherer, Nat. Mater. 3, 601 (2004).
[2] K. Okamotoa, M. Funatob, Y. Kawakamib, K. Tamada, J. Photochem. Photobiol. C, 32, 58 (2017).
[3] K. Okamoto, D. Tanaka, R. Degawa, X. Li, P. Wang, S. Ryuzaki, and K. Tamada, Sci. Rep. 6, 36165 (2016).
