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Title: Plasmonic nanoclusters with rotational symmetry: Polarization-invariant far-field response vs changing near-field distribution
Authors: Rahmani, M.
Yoxall, E.
Hopkins, B.
Sonnefraud, Y.
Kivshar, Y.
Hong, M. 
Phillips, C.
Maier, S.A.
Miroshnichenko, A.E.
Keywords: near-field optical microscopy
plasmonic oligomers
polarization independence
Issue Date: 23-Dec-2013
Citation: Rahmani, M., Yoxall, E., Hopkins, B., Sonnefraud, Y., Kivshar, Y., Hong, M., Phillips, C., Maier, S.A., Miroshnichenko, A.E. (2013-12-23). Plasmonic nanoclusters with rotational symmetry: Polarization-invariant far-field response vs changing near-field distribution. ACS Nano 7 (12) : 11138-11146. ScholarBank@NUS Repository.
Abstract: 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. © 2013 American Chemical Society.
Source Title: ACS Nano
ISSN: 19360851
DOI: 10.1021/nn404869c
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