Kim Yeonhong, Baek Seunghwa, Gupta Prince, Kim Changwook, Chang Kiseok, Ryu Sung-Pil, Kang Hansaem, Kim Wook Sung, Myoung Jaemin, Park Wounjhang, Kim Kyoungsik
School of Mechanical Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul, 03722, Republic of Korea.
Technology Collaboration Team, LG Display Co., Ltd., Gyeonggi-do, 413-811, Republic of Korea.
Sci Rep. 2019 Feb 19;9(1):2265. 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.
表面等离子体近场与传感介质的耦合是基于表面等离子体的传感装置灵敏度的关键。传感介质需要是低折射率电介质，以支持能够深入电介质介质的高穿透性表面等离子体倏逝场。气凝胶衬底的类空气折射率n为超低折射率等离子体装置提供了另一个维度。在本文中，我们通过实验观察到，超低折射率气凝胶衬底在74°处出现了角表面等离子体共振凹陷，这与理论预期一致。我们还展示了相对高灵敏度的表面等离子体共振波长λ，同时详细研究了不同衬底的Δλ/Δn变化。在气凝胶（n = 1.08）和聚二甲基硅氧烷（PDMS；n = 1.4）衬底上刻有周期为740 nm的金属光栅。在光栅上以反射模式观察紫外-可见-近红外光谱，气凝胶和PDMS衬底的灵敏度分别为740.2和655.9 nm/RIU。进行了数值模拟以了解表面等离子体的近场，模拟结果表明共振与实验观察结果高度相关。当使用低折射率衬底时，观察到由表面等离子体激元激发产生的近场更加受限且能更深入地穿透传感介质。
