Giant Tunable Circular Dichroism of Large-Area Extrinsic Chiral Metal Nanocrescent Arrays

Abstract

Circular dichroism (CD) is an interesting phenomenon originating from the interaction of light with chiral molecules or other nanostructures lacking mirror symmetries in three-dimensional (3D) or two-dimensional (2D) space. While the observable effects of optical chirality are very weak in most of the natural materials, they can be designed and significantly enhanced in synthetic chiral structures, where the spatial symmetry of their component are broken on a nanoscale. Therefore, fabrication of composites capable of cheap, time-saving, and giant CD is desirable for the advanced optical technologies. Here, the giant CD of large-area metal nanocrescent array structures was investigated theoretically and experimentally. The largest value of the CD spectrum measured was larger than 0.5, and the CD spectrum was tuned effectively and extensively while maintaining a large peak intensity, which can be attributed to the selective excitation of the lattice surface modes (LSMs) by circularly polarized light. The analysis of the extrinsic chiral structure shows potential applications in chiral molecule sensing and polarizing imaging.

Chiral Surface Lattice Resonances

“…[ 7,8 ] The spectral position of these SLRs can be tuned by the angle of incidence, leading to the emergence of extrinsic chiral surface lattice resonances. [ 9–12 ] Strong optical activity can also result from plasmonic 3D nanostructures without mirror symmetry. However, SLRs from arrays of 3D building‐blocks with intrinsic chirality remain unexplored, but promise decreased losses and enhanced optical activity.…”

“…For conventional colloidal lithography processes, which depend on the controlled shrinkage of a polymer particle matrix, such distances are not easily achievable. [ 12,28–30 ] Therefore, we use core–shell particles with rigid cores (silica) and soft, deformable polymer shells. [ 31,32 ] The particles self‐assemble into hexagonally ordered monolayers at the air/water interface, where the polymer shell provides a flexible spacer to separate the inorganic core particles.…”

The Beginner's Guide to Chiral Plasmonics: Mostly Harmless Theory and the Design of Large‐Area Substrates

“…Reproduced under the terms of Creative Commons (CC BY) license. [ 188 ] Copyright 2019, The Authors, published by Springer Nature. b) Planar chiral structures break the symmetry via the underlying substrate.…”

“…Spectral shifts with rotation angle result from surface lattice resonances caused by the arraying of the crescents in a defined lattice. Reproduced under the terms of Creative Commons (CC BY) license [188]. Copyright 2019, The Authors, published by Springer Nature.…”

Well‐Defined Nanostructures for Electrochemical Energy Conversion and Storage

“…In conjunction with numerous material-synthesis approaches, highly ordered nanostructure arrays can be easily obtained which are characterized by different shapes and broad size ranges (Figure 6b). For example, by taking advantage of PVD, honey-comb arrayed nanodots of various materials are obtainable through perpendicular evaporation onto the PS template: [98,99] if the material evaporation is performed with an angle with respect to the PS template, arrays of crescent-like nanostructures are synthesized; [100] performing evaporation, as the PS template is rotated at a certain rate, leads to arrayed nanorings; [101] if one performs dry etching to shrink PS size before PVD, 2D nanomeshes with tunable pore sizes can be deposited and exploited after removing the PS spheres. [102] In addition to 0D nanoparticles and 2D nanomeshes, highly ordered 1D nanostructures such as Si nanowires are obtainable by combining PS templates and a dry-etching process in which the arrangement of PS spheres defines the spatial configuration of the nanowire array on the Si-wafer surface.…”