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.
Bibliographical noteFunding Information:
This research was supported by the Global Research Lab. (GRL) Program, the Pioneer Research Center Program, a grant from the National Research Foundation (NRF) of Korea funded by the Ministry of Science, ICT & Future Planning (NRF-2016K1A1A2912758, NRF-2013M3C1A3065045, NRF-2018R1A2A2A05020674), the Center for Advanced Meta-Materials(CAMM-2014M3A6B3063712) funded by the Ministry of Science, ICT and Future Planning as Global Frontier Project, and from LG Display under LGD-Yonsei University Incubation Program.
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