Transition from localized surface plasmon resonance to extended surface plasmon-polariton as metallic nanoparticles merge to form a periodic hole array

W. A. Murray, S. Astilean, and W. L. Barnes
Phys. Rev. B 69, 165407 – Published 19 April 2004
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Abstract

We present results of experiments to determine the dispersion of the plasmon modes associated with periodic silver nanoparticle and nanohole arrays fabricated using an extension of the nanosphere lithography technique. Ordered monolayers of polystyrene nanospheres were used as a deposition mask through which silver was deposited by thermal evaporation, subsequent removal of the nanospheres thus leaving an array of metallic nanoparticles. By reactive-ion etching of the nanospheres in an oxygen plasma prior to silver deposition, arrays consisting of particles of increasing size were fabricated. The extremities of the particles eventually merge to create a continuous metallic network perforated by subwavelength holes, thus allowing a study of the particle-hole transition. Combining optical measurements of transmittance and reflectance with information gained using scanning electron microscopy, three separate regimes were observed. For low etch times the samples comprise mainly individual nanoparticles and the optical response is dominated by localized surface plasmon resonances that show no dispersion. As the etch time is increased almost all of the nanoparticles merge with adjacent particles, although many defects are present—notably where some particles fail to merge, a small gap being left between them. The presence of these defects prevents an abrupt structural transition from metallic nanoparticles to a continuous metallic film perforated by an array of nanoholes. The presence of such gaps also results in dispersion data that lack clearly defined features. A further increase in etch time leads to samples with no gaps: instead, a continuous metal film perforated by a nanohole array is produced. The optical response of these structures is dominated by extended surface plasmon-polariton modes.

  • Received 31 October 2003

DOI:https://doi.org/10.1103/PhysRevB.69.165407

©2004 American Physical Society

Authors & Affiliations

W. A. Murray1, S. Astilean2, and W. L. Barnes1

  • 1School of Physics, University of Exeter, Exeter, EX4 4QL, United Kingdom
  • 2Optics and Spectroscopy Department, Faculty of Physics, 3400 Cluj Napoca, Romania

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Vol. 69, Iss. 16 — 15 April 2004

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