Abstract
We numerically study the effect of the symmetry breaking on surface plasmon (SP) modes in two-dimensional dense arrays of truncated metal nanoshells (nanocups), by investigating light transmission through the arrays. We show that localized spherelike and voidlike Mie SP modes, and delocalized Bragg-type SP modes in complete nanoshell arrays become progressively weak and finally disappear when the opening angle of nanocups is increased to tens of degrees. Under higher degree of symmetry breaking, however, the coupling between spherelike and voidlike SP modes leads to an enhancement of SP resonances even though these modes are weakly excited, due to the large optical cross section of voidlike modes. Energy variations of the hybridized mode versus the opening angle are well predicted using a plasmon standing wave model. Furthermore, disappeared Bragg-type SP modes could be re as a result of near-field coupling via hot spots around the rims of nanocups.
Highlights
Optical properties of individual metallic nanoparticles (NPs) and their ensembles have been the subject of intense research because they can support localized surface plasmon (SP) resonances
It is well known that surface plasmon polaritons (SPPs) waves propagating along a planar surface of metal cannot be directly coupled to incoming light
We have investigated variations of optical transmission properties as a 2D HCP metallic nanoshell array is progressively evolves into a semi-shell array
Summary
Optical properties of individual metallic nanoparticles (NPs) and their ensembles have been the subject of intense research because they can support localized surface plasmon (SP) resonances. Symmetry-broken semishells [17,18,19,20,21,22,23,24,25,26,27,28,29] have aroused increasing interest due to their highly tunable plasmonic properties and interesting plasmon modes, such as the anti-bonding mode which has been experimentally verified [24] These approaches suggest potential applications, for example, surface-enhanced Raman spectroscopy substrates for molecular detection [22,23,24,25,29]. Caused by the symmetry-breaking of nanoshells, the two localized modes are only weakly excited, if they are not in resonance in spectrum When they are tuned close to each other, an enhanced transmission is mediated as a result of the excitation of a hybridized mode, which can be manipulated by controlling the dielectric constant of the inside and outside media of nanocups. We have found that delocalized Bragg-type plasmons vanish when the perturbation to the electromagnetic field distribution becomes large enough due to broken symmetry, they can still be re-established under large opening angles via the excitation of hot spots around the metal rims created by the opening
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