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Low-cost and large-scale fabrication of 3D chiral metamaterials is highly desired for potential applications such as nanophotonics devices and chiral biosensors. One of the promising fabrication methods is to use glancing angle deposition (GLAD) of metal on self-assembled dielectric microsphere array. However, structural handedness varies locally due to long-range disorder of the array and therefore large-scale realization of the same handedness is impossible. Here, using symmetry considerations a two-step GLAD process is proposed to eliminate this longstanding problem. In the proposed scheme, the unavoidable long-range disorder gives rise to microscale domains of the same handedness but of slightly different structural geometries and ultimately contributes to a broad-band response. Experimentally, a record-breaking superchiral response of circular dichroism signal of ≈11° is demonstrated and an average polarization rotation angle of 27° in the visible region on ≈1 cm2 sample is observed. Computer-aided geometric reconstruction with experimental parameters unambiguously reveal the presence of strong structural anisotropy and chirality in the prepared stacked-patch plasmonic chiral metamaterial; microscopic spectral analyses combined with full-wave electromagnetic simulations coherently provide deeper insights into the measured circular dichroism and optical activity. The observed chiroptical response can also be flexibly controlled by adjusting the deposition parameters for various potential applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] The possibilities to produce precisely-controlled nanoparticle groupings by using biological and polymeric spacers are discussed. [•] Experimental data are used to point out the current limits of forming gold nanoparticle dimers by using biological and polymeric spacers. [•] Calculations were made to discuss the effect of the nanoparticle diameter and the inter-particle distance in the plasmonic coupling. [ABSTRACT FROM AUTHOR]

Plasmonic resonances with a Fano lineshape observed in metallic nanoclusters often arise from the destructive interference between a dark, subradiant mode and a bright, super-radiant one. A flexible control over the Fano profile characterized by its linewidth and spectral contrast is crucial for many potential applications such as slowing light and biosensing. In this work, we show how one can easily but significantly tailor the overall spectral profile in plasmonic nanocluster systems, for example, quadrumers and pentamers, by selectively altering the particle shape without a need to change the particle size, interparticle distance, or the number of elements of the oligomers. This is achieved through decomposing the whole spectrum into two separate contributions from subgroups, which are efficiently excited at their spectral peak positions. We further show that different strengths of interference between the two subgroups must be considered for a full understanding of the resulting spectral lineshape. In some cases, each subgroup is separately active in distinct frequency windows with only small overlap, leading to a simple convolution of the subspectra. Variation in particle shape of either subgroup results in the tuning of the overall spectral lineshape, which opens a novel pathway for shaping the plasmonic response in small nanoclusters. [ABSTRACT FROM AUTHOR]