Real-space mapping of tailored sheet and edge plasmons in graphene nanoresonators

Journal name:
Nature Photonics
Volume:
10,
Pages:
239–243
Year published:
DOI:
doi:10.1038/nphoton.2016.44
Received
Accepted
Published online

Plasmons in graphene nanoresonators have many potential applications in photonics and optoelectronics, including room-temperature infrared and terahertz photodetectors, sensors, reflect arrays or modulators1, 2, 3, 4, 5, 6, 7. The development of efficient devices will critically depend on precise knowledge and control of the plasmonic modes. Here, we use near-field microscopy8, 9, 10, 11 between λ0 = 10–12 μm to excite and image plasmons in tailored disk and rectangular graphene nanoresonators, and observe a rich variety of coexisting Fabry–Perot modes. Disentangling them by a theoretical analysis allows the identification of sheet and edge plasmons, the latter exhibiting mode volumes as small as 10−8λ03. By measuring the dispersion of the edge plasmons we corroborate their superior confinement compared with sheet plasmons, which among others could be applied for efficient 1D coupling of quantum emitters12. Our understanding of graphene plasmon images is a key to unprecedented in-depth analysis and verification of plasmonic functionalities in future flatland technologies.

At a glance

Figures

  1. GP modes in graphene disk nanoresonators on an SiO2 substrate.
    Figure 1: GP modes in graphene disk nanoresonators on an SiO2 substrate.

    a,b, Schematics of the experiment (a) and simulation model (b). c,d, Experimental (c) and simulated (d) near-field images at the wavelengths λ0,1 = 11.06 μm and λ0,2 = 11.31 μm. e, Schematics illustrating the constructive and destructive interference of the dipole's near field (Esub) and the GP field (EGP), respectively, yielding the peak c1 in i, and peak e2 in j. f, Near-field distributions 15 nm above the graphene disks induced by the dipole located at either the centre (denoted by c1, c2) or the edge (denoted by e1, e2, e3 and e4). The dipole locations are marked by green dots. They correspond to the modes c1, c2 and e1–e4 marked by black dots in i and j. gj, Measured and calculated near-field magnitude in the disk centre and at the edge for λ0,1 and λ0,2. Simulations assume EF = 0.33 eV and τ = 0.1 ps.

  2. GP modes in rectangular graphene nanoresonators on a 5-nm-thick SiO2 film on a CaF2 substrate.
    Figure 2: GP modes in rectangular graphene nanoresonators on a 5-nm-thick SiO2 film on a CaF2 substrate.

    ac, Topography (top left), experimental near-field image (|Es|, top right), calculated near-field image (|Ez|, middle right) and calculated near-field distributions when the dipole is placed at positions marked by green dot for different resonator sizes: 394 × 73 nm (a), 360 × 180 nm (b) and 400 × 450 nm (c). λ0 = 11.31 μm (marked by the vertical green line in df). w1 marks the fundamental waveguiding mode, s1–s3 mark the first-order to third-order transversal sheet mode and e1–e4 mark the first-order to fourth-order edge modes. df, Corresponding near-field spectra calculated at the points A–F (marked by green dots in the near-field distributions) for the resonators shown in ac. To provide the closest match between the experimental and simulated near-field images we used Fermi energies of EF = 0.30 eV (a,d), EF = 0.28 eV (b,e) and EF = 0.31 eV (c,f). Relaxation time τ = 0.1 ps.

  3. Dispersion of sheet and edge GPs in a large graphene structure on an SiO2 substrate.
    Figure 3: Dispersion of sheet and edge GPs in a large graphene structure on an SiO2 substrate.

    a, Experimental near-field image at λ0 = 11.31 μm. b, The dashed curves represent the individual line profiles along the horizontal white line in a, and solid curves represent averages of 20 individual line profiles in proximity to the solid white line in a. c, Averaged ratio Δp/Δe obtained from individual near-field profiles such as the ones shown in b. The error bars show the standard deviation, and the line shows the calculated ratio λp/λe. d, Calculated near-field image. e, The near-field distribution generated by a dipole placed above the graphene rectangle at the position marked by the green dot. f, Dispersion (lines for the theory and symbols for the experiment) of the sheet and edge GPs. Simulations assume EF = 0.33 eV and τ = 0.1 ps. Experimental data for λ0 < 10.6 μm are missing, because λp could not be measured.

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Author information

Affiliations

  1. CIC nanoGUNE, 20018 Donostia-San Sebastián, Spain

    • A. Y. Nikitin,
    • P. Alonso-González,
    • S. Vélez,
    • S. Mastel,
    • F. Casanova &
    • L. E. Hueso
  2. IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain

    • A. Y. Nikitin,
    • F. Casanova,
    • L. E. Hueso &
    • R. Hillenbrand
  3. Institute of Physics, Chinese Academy of Science, Beijing 100190, China

    • P. Alonso-González
  4. Graphenea SA, 20018 Donostia-San Sebastián, Spain

    • A. Centeno,
    • A. Pesquera &
    • A. Zurutuza
  5. ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain

    • F. H. L. Koppens
  6. ICREA – Institució Catalana de Recerça i Estudis Avancats, E-08010 Barcelona, Spain

    • F. H. L. Koppens
  7. CIC NanoGUNE and UPV/EHU, 20018 Donostia-San Sebastian, Spain

    • R. Hillenbrand

Contributions

A.Y.N., P.A.G. and R.H. conceived the study. S.V. patterned the graphene nanoresonators. A.C. and A.P. prepared the CVD graphene. A.Z., F.C. and L.E.H. coordinated the fabrication. P.A.G. and S.M. performed the experiments. A.Y.N. developed the theory and performed the simulations. A.Y.N., P.A.G., F.H.L.K. and R.H. analysed the data and discussed the results. A.Y.N. and R.H. wrote the manuscript with the input of P.A.G. All authors contributed to the scientific discussion and manuscript revisions.

Competing financial interests

R.H. is a co-founder of Neaspec GmbH, a company producing scattering-type scanning near-field optical microscope systems such as the one used in this study. All other authors declare no competing financial interests.

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