4.7 Article

Beyond-hot-spot absorption enhancement on top of terahertz nanotrenches

期刊

NANOPHOTONICS
卷 11, 期 13, 页码 3159-3167

出版社

WALTER DE GRUYTER GMBH
DOI: 10.1515/nanoph-2022-0214

关键词

absorption; field enhancement; hot spots; nanogaps; terahertz

资金

  1. National Research Foundation (NRF) of Korea Government [MSIT: NRF-2021R1C1C1010660, MSIP: NRF-2015R1A3A2031768]
  2. Kangwon National University
  3. UNIST (Ulsan National Institute of Science Technology) [1.190055.01]
  4. National Research Foundation of Korea (NRF) - Korean government [NRF-2021R1A2C1008452]
  5. Ulsan National Institute of Science and Technology (UNIST) [1.220061.01, 1.190098.01]

向作者/读者索取更多资源

Metallic nanogaps are widely used for sensing applications due to their ability to confine and enhance electromagnetic field within the hot spots. This study extends the concept of near field absorption enhancement by analyzing the terahertz absorption behavior of water molecules outside the hot spots of sub-20 nm-wide nanotrenches. The findings provide means to quantitatively analyze light-matter interactions beyond the hot spot picture and enable the application of nanogaps for sensitive surface analyses.
Metallic nanogaps are being widely used for sensing applications, owing to their ability to confine and enhance electromagnetic field within the hot spots. Since the enhanced field does not confine itself perfectly within the gap, however, fringe fields well away from the gap are of potential use as well in real systems. Here, we extend the concept of near field absorption enhancement by quantitatively analyzing terahertz absorption behavior of water molecules outside the hot spots of sub-20 nm-wide, similar to 100 mu m-long nanotrenches. Contrary to point-gaps which show negligible field enhancement at distances larger than the gap width, our extended nanogap act as a line source, incorporating significant amount of absorption enhancement at much longer distances. We observe absorption enhancement factors of up to 3600 on top of a 5 nm-wide gap, and still well over 300 at 15 nm away. The finding is well supported by theoretical analyses including modal expansion calculations, Kirchhoff integral formalism and antenna theory. Our results provide means to quantitatively analyze light-matter interactions beyond the hot spot picture and enable application of nanogaps for sensitive surface analyses of various material systems.

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