An acoustic plasmon mode in a graphene-dielectric-metal structure has recently been spotlighted as a superior platform for strong light-matter interaction. It originates from the coupling of graphene plasmon with its mirror image and exhibits the largest field confinement in the limit of a sub-nm-thick dielectric. Although recently detected in the far-field regime, optical near-fields of this mode are yet to be observed and characterized. Here, we demonstrate a direct optical probing of the plasmonic fields reflected by the edges of graphene via near-field scattering microscope, revealing a relatively small propagation loss of the mid-infrared acoustic plasmons in our devices that allows for their real-space mapping at ambient conditions even with unprotected, large-area graphene grown by chemical vapor deposition. We show an acoustic plasmon mode that is twice as confined and has 1.4 times higher figure of merit in terms of the normalized propagation length compared to the graphene surface plasmon under similar conditions. We also investigate the behavior of the acoustic graphene plasmons in a periodic array of gold nanoribbons. Our results highlight the promise of acoustic plasmons for graphene-based optoelectronics and sensing applications.
Bibliographical noteFunding Information:
This work was supported by the Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-IT1702-14. S.G.M. acknowledges support from the Young Researchers program of the National Research Foundation of Korea (NRF) funded by the Korean government (MSIT) (2019R1C1C1011131). I.-H.L., T.L., and S.-H.O. acknowledge support from the U.S. National Science Foundation (NSF ECCS 1809723). S.-H.O. further acknowledges support from the Samsung Global Research Outreach (GRO) Program and the Sanford P. Bordeau Chair in Electrical Engineering at the University of Minnesota. T.-T.K. acknowledges support from the Priority Research Centers Program through the NRF funded by the Ministry of Education (NRF-2019R1A6A1A11053838). S.L. and Y.H.L. acknowledge support from the Institute for Basic Science of Korea (IBS-R011-D1). Device fabrication was conducted in the Minnesota Nano Center, which is supported by the U.S. National Science Foundation through the National Nano Coordinated Infrastructure Network (NNCI) under Award Number ECCS-2025124.
© 2021, The Author(s).
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