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Probing Far-Infrared Surface Phonon Polaritons in Semiconductor Nanostructures at Nanoscale Ruishi Qi, Renfei Wang, Yuehui Li, Yuanwei Sun, Shulin Chen, Bo Han, Ning Li, Qing Zhang, Xinfeng Liu, Dapeng YU, and Peng Gao Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.9b01350 • Publication Date (Web): 19 Jul 2019 Downloaded from pubs.acs.org on July 21, 2019
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Nano Letters
Probing Far-Infrared Surface Phonon Polaritons in Semiconductor Nanostructures at Nanoscale Ruishi Qi1†, Renfei Wang1†, Yuehui Li1, Yuanwei Sun1, Shulin Chen1, Bo Han1, Ning Li1, Qing Zhang2, Xinfeng Liu3, Dapeng Yu4, and Peng Gao1,5 * 1
International Center for Quantum Materials, and Electron Microscopy Laboratory, School of Physics, Peking University, Beijing 100871, China 2
Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, China 3
Division of Nanophotonics, CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, China 4
Shenzhen Key Laboratory of Quantum Science and Engineering, Shenzhen 518055, China
5
Collaborative Innovation Center of Quantum Matter, and Beijing Key Laboratory of Quantum Devices, Beijing 100871, China. *
Corresponding Author. Correspondence and requests for materials should be addressed to P.G. (
[email protected]) †
These authors contributed equally to this work.
ABSTRACT: Phonon polaritons hold potential prospects of nanophotonic applications at the midand far-infrared wavelengths. However, their experimental investigation in the far-infrared range has long been a technical challenge due to the lack of suitable light sources and detectors. To obviate these difficulties, here we use an electron probe with sub-10 meV energy resolution and subnanometer spatial resolution to study far-infrared surface phonon polaritons (~50–70 meV) in ZnO nanostructures. We observe ultra-slow propagation and interference fringes of propagating surface phonon polaritons, and obtain their dispersion relation through measurements in the coordinate space. By mapping localized modes in nanowires and flakes, we reveal their localized nature and investigate geometry and size effects. Associated with simulation, we show that surface phonon polariton behaviors can be well described by the local continuum dielectric model. Our work paves the way for spatial-resolved investigation of SPhPs by electron probes and forwards polaritonics in the far-infrared range. KEYWORDS: Surface phonon polariton; EELS; STEM; zinc oxide; far infrared; nanophotonics.
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Surface phonon polaritons (SPhPs)1 are highly desirable to extend numerous plasmonic applications in the visible and near-infrared (IR) range facilitated by surface plasmon polaritons (SPPs) to lower frequencies, and to open up unachievable opportunities such as microscopy2 and data storage3. Commonly there are two categories of SPhP modes, i.e., propagating SPhPs that are able to propagate along the surface, and localized surface phonon polaritons (LSPhs) confined to subwavelength vicinity of the surface1. Although many theoretical and numerical works have been done and potential applications of both types have been anticipated in the past decades4-6, their low energy and fine spatial distribution impose stringent requirement on both energy and spatial resolution, making experimental study technically challenging. Based on scattering-type scanning near-field optical microscopy (s-SNOM), recent researches have revealed the nature of mid-IR SPhPs (e.g., in h-BN, SiC, and MoO3) with ~20 nm in spatial resolution7-11. Despite these great advances, s-SNOM is generally limited to two narrow spectral ranges, i.e., the near- to mid-IR range (>70 meV) and the THz range (
