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A nanogroove metasurface for submolecular detection

(Nanowerk News) An international team of researchers has designed a hyperbolic metasurface with metallic nanogroove structure.
As the team reports in Small ("Multifunctional Hyperbolic Nanogroove Metasurface for Submolecular Detection"), this nanogroove metasurface provides multiple functions:
  • 1) To control and manipulate surface plasmon polaritons and modify the wavelength of the surface plasmon waves. The effective permittivity of the metasurface is tunable with the variation of the width and periodicity of the nanogroove structure;
  • 2) To be able to obtain hyperbolic dispersion by tuning the light wavelength in the visible region. As the width and periodicity are fixed at 30 and 150 nm, the nanogroove metasurface shows hyperbolic dispersion at optical wavelengths above 500 nm;
  • 3) The surface plasmon polaritons can propagate along a nondivergent direction as the permittivity of metasurface is in the epsilon-near-zero regime. For the groove nanostructure with the width of 30 nm and the periodicity of 150 nm, the effective refractive index of the metasurface is equal to zero at the ultraviolet wavelength;
  • 4) To achieve ultrahigh sensitivity for plasmonic detection. Even tiny perturbation of the surroundings will lead to a pronounced phase change and related Goos–Hänchen (GH) shift (higher order derivation of phase) of the propagating surface waves.
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    SEM images of the nanogroove hyperbolic metasurface. a) The distribution of the six patches of nanogroove arrays and the coupling grating structure. b) The enlarged view of one patch of nanogroove arrays. Each patch consists of 5 × 5 groove nanostructures. c) The enlarged view of the two adjacent groove nanostructures. d) The detailed view of the groove nanostructure with the width of 30 nm and the periodicity of 150 nm. (© Wiley-VCH Verlag) (click on image to enlarge)
    The authors note that their designed nanogroove hyperbolic metasurface presents strong light–matter interactions that can achieve submolecule detection with ultrahigh sensitivity. The propagations of the surface plasmon waves can be controlled and manipulated by the groove nanostructures.
    The electric field on the sensing surface is significantly enhanced due to the highly confined surface plasmons in the plane and the increased local density of states on the groove ridge.
    The perfect absorption can be achieved due to the constructive interference and increased damping constant of the hyperbolic metasurface.
    By tuning the optical frequency, surface plasmon waves can be tightly confined and propagating in a diffraction-free direction induced by the zero refractive index.
    "These significant performances of the nanogroove metasurface would allow the creation of on-chip multifunctional photonic and optoelectronic devices for biosensing, imaging, and quantum communication," the researchers conclude.
    Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
    Nano-Society: Pushing the Boundaries of Technology,
    Nanotechnology: The Future is Tiny, and
    Nanoengineering: The Skills and Tools Making Technology Invisible
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