Raspberry-like metamolecules exhibiting strong magnetic resonances

Zhaoxia Qian, Simon P. Hastings, Chen Li, Brian Edward, Christine K. McGinn, Nader Engheta, Zahra Fakhraai, So Jung Park

Research output: Contribution to journalArticlepeer-review

79 Scopus citations


We report a synthetic approach to produce raspberry-like plasmonic nanostructures with unusually strong magnetic resonances, termed raspberry-like metamolecules (raspberry-MMs). The synthesis based on the surfactant-assisted templated seed-growth method allows for the simultaneous one-step synthesis and assembly of well-insulated gold nanoparticles. The aromatic surfactant used for the syntheses forms a thin protective layer around the nanoparticles, preventing them from touching each other and making it possible to pack discrete nanoparticles at close distances in a single cluster. The resulting isotropic gold nanoparticle clusters (i.e., raspberry-MMs) exhibit unusually broad extinction spectra in the visible and near-IR region. Finite-difference time-domain (FDTD) modeling showed that the raspberry-MMs support strong magnetic resonances that contribute significantly to the broadband spectra. The strong magnetic scattering was also verified by far-field scattering measurements, which show that in the near-IR region the magnetic dipole resonance can be even stronger than the electric dipole resonance in these raspberry-MMs. Structural parameters such as the size and the number of gold nanoparticles composing raspberry-MMs can be readily tuned in our synthetic method. A series of syntheses with varying structure parameters, along with FDTD modeling and mode analyses of corresponding model structures, showed that the close packing of a large number of metal nanoparticles in raspberry-MMs is responsible for the unusually strong magnetic resonances observed here.

Original languageEnglish
Pages (from-to)1263-1270
Number of pages8
JournalACS Nano
Issue number2
StatePublished - 24 Feb 2015

Bibliographical note

Publisher Copyright:
© 2015 American Chemical Society.


  • gold nanoparticle cluster
  • magnetic dipole
  • magnetic quadrupole
  • magnetic resonance
  • metamaterial
  • metamolecule
  • surface plasmon resonance


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