Chirality and Chiroptical Effects in Metal Nanostructures: Fundamentals and Current Trends

Abstract

Throughout the 19th and 20th century, chirality has mostly been associated with chemistry. However, while chirality can be very useful for understanding molecules, molecules are not well suited for understanding chirality. Indeed, the size of atoms, the length of molecular bonds and the orientations of orbitals cannot be varied at will. It is therefore difficult to study the emergence and evolution of chirality in molecules, as a function of geometrical parameters. By contrast, chiral metal nanostructures offer an unprecedented flexibility of design. Modern nanofabrication allows chiral metal nanoparticles to tune the geometric and optical chirality parameters, which are key for properties such as negative refractive index and superchiral light. Chiral meta/nano‐materials are promising for numerous technological applications, such as chiral molecular sensing, separation and synthesis, super‐resolution imaging, nanorobotics, and ultra‐thin broadband optical components for chiral light. This review covers some of the fundamentals and highlights recent trends. We begin by discussing linear chiroptical effects. We then survey the design of modern chiral materials. Next, the emergence and use of chirality parameters are summarized. In the following part, we cover the properties of nonlinear chiroptical materials. Finally, in the conclusion section, we point out current limitations and future directions of development.

Large‐Area 3D Plasmonic Crescents with Tunable Chirality

“…The resulting geometry differs from planar asymmetric crescent structures, which show a dependence of the chiroptical response on the illumination direction . Planar chiral structures in general may exhibit true chirality only due to the substrate induced symmetry breaking or fabrication imperfections . Residuals of the templating polymer spheres, visible in the centre of the crescent (Figure b), do not affect significantly the optical properties and may be removed by immersion in organic solvents.…”

“…Chirality is a fundamental property describing structures that cannot be superimposed with their mirror images. While ubiquitous on the molecular scale, chirality has only recently been identified as an important tool to tailor the optical properties of plasmonic nanostructures …”

“…Motivated by these applications, a range of complex nanostructures with extraordinary chiral properties has recently emerged . Such structures include stacked split‐ring resonators, nanohelices, plasmonic dimers/oligomers, DNA‐based materials, structures fabricated by on‐edge lithography, and planar symmetric heterotrimers …”

Switching of Giant Lateral Force on Sub‐10 nm Particle Using Phase‐Change Nanoantenna

“…[1] Recently, the increasing trend toward nanotechnology and nanomedicine has created a demand for applications of this non-invasive technique on the nanometer scale. [10][11][12][13][14][15] Such a strategy can overcome the diffraction limit since the optical trapping is based on localized surface plasmon resonances (LSPR) rather than propagating electromagnetic (EM) waves. [2][3][4][5] This drawback can be overcome with plasmonic nanoapertures in metallic films [6,7] and planar waveguides [8] where the nanostructures can produce a giant near-field gradient in the subwavelength area, [9] enabling precise trapping, manipulation, and characterization of nanoparticles.…”

Circular Dichroism in Higher‐Order Diffraction Beams from Chiral Quasiplanar Nanostructures

“…[5][6][7][8][9][10] Several relevant reviews have been published recently. [11][12][13] Circular dichroism (CD) is routinely used to investigate chiral nanomaterials, which absorb and scatter left-and right-circularly polarized light (LCP and RCP) differently depending on the handedness of the nanostructures. Such nanostructures can give rise to much stronger CD than chiral molecules, in part because the pitch of the twist is better matched to optical wavelengths.…”