Abstract
Collective excitation of periodic arrays of metallic nanoparticles by coupling localized surface plasmon resonances to grazing diffraction orders leads to surface lattice resonances with narrow line width. These resonances may find numerous applications in optical sensing and information processing. Here, a new degree of freedom of surface lattice resonances is experimentally investigated by demonstrating handedness-dependent excitation of surface lattice resonances in arrays of chiral plasmonic crescents. The self-assembly of particles used as mask and modified colloidal lithography is applied to produce arrays of planar and 3D gold crescents over large areas. The excitation of surface lattice resonances as a function of the interparticle distance and the degree of order within the arrays is investigated. The chirality of the individual 3D crescents leads to the formation of chiral lattice modes, that is, surface lattice resonances that exhibit optical activity.
Highlights
Collective excitation of periodic arrays of metallic nanoparticles by coupling resonances.[5,6] A collective excitation (SLR) possesses a reduced linewidth as localized surface plasmon resonances to grazing diffraction orders leads to compared to the excitation of the LSPRs surface lattice resonances with narrow line width
The self-assembly surfaces constructed of an array of of particles used as mask and modified colloidal lithography is applied to split-ring resonators showed that produce arrays of planar and 3D gold crescents over large areas
The chirality of the individual 3D crescents leads to the formation of chiral lattice modes, that is, SLRs can selectively respond to the handedness of circularly polarized light, causing sharp lattice-mode assisted extrinsic circular dichroism.[7,8]
Summary
We can produce nanostructure arrays with large interparticle distances required to observe SLRs. We experimentally confirm the feasibility of our methods by fabricating arrays of 3D crescents with controlled interparticle distances resulting in the appearance of chiral SLRs. We use core–shell particles consisting of SiO2 cores (d = 198 nm) with soft poly(N-isopropylacrylamide) (PNiPAm) shells (Figure 1a) and self-assemble them at the air/water interface of a Langmuir trough.[33] The soft PNiPAm shell separates the silica cores, which form a non-close-packed hexagonal lattice. If the interparticle distances of the arrays are too small, the resonances broaden compared to individual spectra.[47] At Dhex > 600 nm, the grazing diffraction orders start to couple to the localized U1 resonance and U-SLRs are observed due to sufficient spectral overlap of the two resonances. We first investigated the excitation of SLRs in achiral crescents as a function of the lattice constant of the array and correlate their spectral properties with the degree of order in the sample. The presented chiral 3D-metasurfaces may find applications in enhanced chiral sensing, handedness-selective coupling to guided modes, control of circularly polarized fluorescence emission, or the design of polarization-selective mirrors
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