The fundamental optical properties of pure nickel nanostructures are studied by far-field extinction spectroscopy and optical near-field microscopy, providing direct experimental evidence of the existence of particle plasmon resonances predicted by theory. Experimental and calculated near-field maps allow for unambiguous identification of dipolar plasmon modes. By comparing calculated near-field and far-field spectra, dramatic shifts are found between the near-field and far-field plasmon resonances, which are much stronger than in gold nanoantennas. Based on a simple damped harmonic oscillator model to describe plasmonic resonances, it is possible to explain these shifts as due to plasmon damping. Experimental evidence of plasmon resonances in pure nickel nanoantennas is provided by both far-field spectroscopy and near-field microscopy. Ultra-high resolution near-field microscopy visualizes the dipole plasmon modes in nickel disks as well as the transverse plasmon mode of elongated nickel nanoantennas. The shifts between far- and near-field spectra of plasmonic antennas are also elucidated, which points out the need of taking into account both near- and far-field properties when designing nanophotonic devices. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- magnetic nanoparticles
- near-field optical imaging
- optical antennas
- scattering-type scanning near-field optical microscopy