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

• Published in: Scientific reports Vol. 9; no. 1; p. 2265
• Main Authors: Kim, Yeonhong, Baek, Seunghwa, Gupta, Prince, Kim, Changwook, Chang, Kiseok, Ryu, Sung-Pil, Kang, Hansaem, Kim, Wook Sung, Myoung, Jaemin, Park, Wounjhang, Kim, Kyoungsik
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 19.02.2019; Nature Publishing Group UK
• Subjects: Electromagnetism; Polydimethylsiloxane; Scanning electron microscopy; Sensors; Silica; Silver; Surface plasmon resonance; Surfactants
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-38859-2

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.