Air-like plasmonics with ultralow-refractive-index silica aerogels

Yeonhong Kim, Seunghwa Baek, Prince Gupta, Changwook Kim, Kiseok Chang, Sung Pil Ryu, Hansaem Kang, Wook Sung Kim, Jaemin Myoung, Wounjhang Park, Kyoungsik Kim

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Abstract

The coupling of the surface plasmon near-field into the sensing medium is key to the sensitivity of surface plasmon-based sensing devices. A low-index dielectric is necessary for the sensing medium to support a highly-penetrating surface plasmon evanescent field that extends well into the dielectric medium. The air-like refractive index, n, of an aerogel substrate provides another dimension for ultralow-index plasmonic devices. In this paper, we experimentally observed an angular surface plasmon resonance dip at 74° with the ultralow-index aerogel substrate, as was expected from theory. We also demonstrated the comparatively high-sensitivity surface plasmon resonance wavelength, λ, while the change in Δλ/Δn with different substrates was studied in detail. A 740 nm-period metal grating was imprinted on aerogel (n = 1.08) and polydimethylsiloxane (PDMS; n = 1.4) substrates. The ultraviolet–visible–near-infrared spectra were observed in the reflection mode on the grating, resulting in sensitivities of 740.2 and 655.9 nm/RIU for the aerogel and PDMS substrates, respectively. Numerical simulations were performed to understand the near-field of the surface plasmon, which demonstrated resonances well correlated with the experimentally observed results. The near-field due to excitation of the surface plasmon polaritons is observed to be more confined and to penetrate deeper into the sensing medium when a low-index substrate is used.

Original languageEnglish
Article number2265
JournalScientific reports
Volume9
Issue number1
DOIs
Publication statusPublished - 2019 Dec 1

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Kim, Y., Baek, S., Gupta, P., Kim, C., Chang, K., Ryu, S. P., Kang, H., Kim, W. S., Myoung, J., Park, W., & Kim, K. (2019). Air-like plasmonics with ultralow-refractive-index silica aerogels. Scientific reports, 9(1), [2265]. https://doi.org/10.1038/s41598-019-38859-2