Plasmonic nanoclusters with rotational symmetry: Polarization-invariant far-field response vs changing near-field distribution

Mohsen Rahmani, Edward Yoxall, Ben Hopkins, Yannick Sonnefraud, Yuri Kivshar, Minghui Hong, Chris Phillips, Stefan A. Maier, Andrey E. Miroshnichenko

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53 Citations (Scopus)


Flexible control over the near- and far-field properties of plasmonic nanostructures is important for many potential applications, such as surface-enhanced Raman scattering and biosensing. Generally, any change in the polarization of the incident light leads to a change in the nanoparticle's near-field distribution and, consequently, in its far-field properties as well. Therefore, producing polarization-invariant optical responses in the far field from a changing near field remains a challenging issue. In this paper, we probe experimentally the optical properties of cruciform pentamer structures - as an example of plasmonic oligomers - and demonstrate that they exhibit such behavior due to their symmetric geometrical arrangement. We demonstrate direct control over hot spot positions in sub-20 nm gaps, between disks of 145 nm diameter at a wavelength of 850 nm, by means of scattering scanning near-field optical microscopy. In addition, we employ the coupled dipole approximation method to define a qualitative model revealing the relationship between the near and far field in such structures. The near-field profiles depend on particular mode superpositions excited by the incident field and, thus, are expected to vary with the polarization. Consequently, we prove analytically that the far-field optical properties of pentamers have to be polarization-independent due to their rotational symmetry.

Original languageEnglish
Pages (from-to)11138-11146
Number of pages9
JournalACS Nano
Issue number12
Publication statusPublished - 23 Dec 2013
Externally publishedYes


  • near-field optical microscopy
  • plasmonic oligomers
  • polarization independence
  • symmetry

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