Mastering the manipulation of chirality at the nanoscale has long been a priority for chemists, physicists, and materials scientists, given its importance in the biochemical processes of the natural world and in the development of novel technologies. In this vein, the formation of novel metamaterials and sensing platforms resulting from the synergic combination of chirality and plasmonics has opened new avenues in nano-optics. Recently, the implementation of chiral plasmonic nanostructures in photocatalysis has been proposed theoretically as a means to drive polarization-dependent photochemistry. In the present work, we demonstrate that the use of inorganic nanometric chiral templates for the controlled assembly of Au and TiO 2 nanoparticles leads to the formation of plasmon-based photocatalysts with polarization-dependent reactivity. The formation of plasmonic assemblies with chiroptical activities induces the asymmetric formation of hot electrons and holes generated via electromagnetic excitation, opening the door to novel photocatalytic and optoelectronic features. More precisely, we demonstrate that the reaction yield can be improved when the helicity of the circularly polarized light used to activate the plasmonic component matches the handedness of the chiral substrate. Our approach may enable new applications in the fields of chirality and photocatalysis, particularly toward plasmon-induced chiral photochemistry.

Plasmonic nanocrystals and their assemblies are excellent tools to create functional systems, including systems with strong chiral optical responses. Here we study the possibility of growing chiral plasmonic nanocrystals from strictly nonchiral seeds of different types by using circularly polarized light as the chirality-inducing mechanism. We present a novel theoretical methodology that simulates realistic nonlinear and inhomogeneous photogrowth processes in plasmonic nanocrystals, mediated by the excitation of hot carriers that can drive surface chemistry. We show the strongly anisotropic and chiral growth of oriented nanocrystals with lowered symmetry, with the striking feature that such chiral growth can appear even for nanocrystals with subwavelength sizes. Furthermore, we show that the chiral growth of nanocrystals in solution is fundamentally challenging. This work explores new ways of growing monolithic chiral plasmonic nanostructures and can be useful for the development of plasmonic photocatalysis and fabrication technologies.

High index dielectric nanoparticles have been proposed for many different applications. However, widespread utilization in practice also requires large-scale production methods for crystalline silicon nanoparticles, with engineered optical properties in a low-cost manner.Here, we demonstrate a facile, low-cost, and large-scale fabrication method of crystalline silicon colloidal Mie resonators in water, using a blender. The obtained nanoparticles are polydisperse with an almost spherical shape and the diameters controlled in the range 100−200 nm by a centrifugation process. Then the size distribution of silicon nanoparticles enables broad extinction from UV to near-infrared, confirmed by Mie theory when considering the size distribution in the calculations. Thanks to photolithographic and drop-cast deposition techniques to locate the position on a substrate of the colloidal nanoparticles, we experimentally demonstrate that the individual silicon nanoresonators show strong electric and magnetic Mie resonances in the visible range.

In plasmonics, and particularly in plasmonic photochemistry, the effect of hotelectron generation is an exciting phenomenon driving new fundamental and applied research.However, obtaining a microscopic description of the hot-electron states represents a challenging problem, limiting our capability to design efficient nanoantennas exploiting these excited carriers. This paper addresses this limitation and studies the spatial distributions of the photophysical dynamic parameters controlling the local surface photochemistry on a plasmonic nanocrystal. We found that the generation of energetic electrons and holes in small plasmonic nanocrystals with complex shapes is strongly position-dependent and anisotropic, whereas the 2 phototemperature across the nanocrystal surface is nearly uniform. Our formalism includes three mechanisms for the generation of excited carriers: the Drude process, the surface-assisted generation of hot-electrons in the sp-band, and the excitation of interband d-holes. Our computations show that the hot-carrier generation originating from these mechanisms reflects the internal structure of hot spots in nanocrystals with complex shapes. The injection of energetic carriers and increased surface phototemperature are driving forces for photocatalytic and photo-growth processes on the surface of plasmonic nanostructures. Therefore, developing a consistent microscopic theory of such processes is necessary for designing efficient nanoantennas for photocatalytic applications.

This Perspective concerns the latest developments in the field of chiral nanocrystals (NCs) and metastructures, focusing primarily on plasmonic nanostructures. Such nanomaterials exhibit unusually strong near-field and electromagnetic responses that enable efficient biosensing and light manipulation. Herein we share our thoughts on the latest trends that mark what we call a paradigm shift for the vast and dynamic field of chiroptical materials. The topics to be considered include polarization-sensitive photocatalysis with chiral plasmonic NCs, chiral bioconjugates, DNA-based assemblies, chiral growth, and we also describe the fundamental challenges for optical induction of chirality, transfer of chirality between different scales, and theoretical issues that nanoscience is facing.

Although the concept of chirality has its origin in chemistry, the field of photonics is actively exploring and utilizing it. A new family of 2D chiral lattices constructed from fully achiral unit cells is introduced here. This type of chiral structure differs fundamentally from previously reported arrays made of chiral unit cells. In this system, circular dichroism (CD) appears due to the electromagnetic interaction between unit cells and the formation of lattice plasmons (LP). Importantly, the CD is strongly enhanced for anisotropic rectangular lattices, whereas the chiral signal in square lattices is found to be relatively weak. The results cover two configurations. The first has an index‐matched environment, and the second includes an asymmetric arrangement of refractive indices. The index‐matched model is preferable and supports ultrasharp LP resonances. Overall, excellent control of the spectral position and broadening of the CD peaks is also demonstrated by tuning the geometry and matrix refractive indices. These results can be useful for engineering polarization filters and chiral biosensors.

Chiral plasmonic nanostructures exhibit anomalously strong chiroptical signals and offer the possibility to realize asymmetric photophysical and photochemical processes controlled by circularly polarized light. Here, we use a chiral DNA-assembled nanorod pair as a model system for chiral plasmonic photomelting. We show that both the enantiomeric excess and consequent circular dichroism can be controlled with chiral light. The nonlinear chiroptical response of our plasmonic system results from the chiral photothermal effect leading to selective melting of the DNA linker strands. Our study describes both the singlecomplex and collective heating regimes, which should be treated with different models. The chiral asymmetry factors of the calculated photothermal and photomelting effects exceed the values typical for the chiral molecular photochemistry at least 10-fold. Our proposed mechanism can be used to develop chiral photoresponsive systems controllable with circularly polarized light.

The optical characterization of a single metallic nanostructure has a strong interest in the scientific community owing to its localized surface plasmon resonances. For a single nano-object, the simplest and the accepted optical characterization technique is dark-field spectroscopy, even if there are many drawbacks and a certain complexity to operate it. We propose here using extinction spectroscopy of nanoparticles ensembles to characterize optically a single nanostructure. The scattering spectrum of a single gold nanocylinder and the extinction spectrum of a well-chosen array show similar results. We perform an experimental and numerical comparative study to draw parallels between both techniques.