posted on 2014-10-15, 00:00authored byRobin Ogier, Yurui Fang, Mikael Svedendahl, Peter Johansson, Mikael Käll
Optical
near-field coupling between closely spaced plasmonic metal nanoparticles
is important to a range of nanophotonic applications of high contemporary
interest, including surface-enhanced molecular spectroscopy, nanooptical
sensing, and various novel light-harvesting concepts. Here we report
on monolayers of chiral heterotrimers and heterotetramers composed
of closely spaced silver and/or gold nanodisks of different heights
fabricated through facile hole-mask colloidal lithography. These quasi-three-dimensional
oligomers are interesting for applications because they exhibit “hot”
gaps and crevices of nanometric dimensions, a pronounced circular
dichroism, and optical chirality in the visible to near-infrared wavelength
range, and they can be produced in large ensembles (>109) of identical orientation. We analyze the optical properties of
the samples based on simulation results and find that the circular
dichroism is due to strong near-field coupling and intricate phase
retardation effects originating in the three-dimensional character
of the individual oligomers.