Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Nonlinear metasurfaces: a paradigm shift in nonlinear optics

Recently, lead halide-based perovskites have become one of the hottest topics in photovoltaic research because of their excellent optoelectronic properties. Among them, organic-inorganic hybrid perovskite solar cells (PSCs) have made very rapid progress with their power conversion efficiency (PCE) now at 23.7 %. However, the intrinsically unstable nature of these materials, particularly to moisture and heat, may be a problem for their long-term stability. Replacing the fragile organic group with more robust inorganic Cs+ cations forms the cesium lead halide system (CsPbX3 , X is halide) as all-inorganic perovskites which are much more thermally stable and often more stable to other factors. From the first report in 2015 to now, the PCE of CsPbX3 -based PSCs has abruptly increased from 2.9 % to 17.1 % with much enhanced stability. In this Review, we summarize the field up to now, propose solutions in terms of development bottlenecks, and attempt to boost further research in CsPbX3 PSCs.

All‐Inorganic CsPbX3 Perovskite Solar Cells: Progress and Prospects

Quantum mechanical interactions between electromagnetic radiation and matter underlie a broad spectrum of optical phenomena. Strong light-matter interactions result in the well-known vacuum Rabi splitting and emergence of new polaritonic eigenmodes of the coupled system. Thanks to recent progress in nanofabrication, observation of strong coupling has become possible in a great variety of optical nanostructures. Here, we review recently studied and emerging materials for realization of strong light–matter interactions. We present general theoretical formalism describing strong coupling and give an overview of various photonic structures and materials allowing for realization of this regime, including plasmonic and dielectric nanoantennas, novel two-dimensional materials, carbon nanotubes, and molecular vibrational transitions. In addition, we discuss practical applications that can benefit from these effects and give an outlook on unsettled questions that remain open for future research.

Novel Nanostructures and Materials for Strong Light–Matter Interactions

Active modulation of electromagnetically induced transparency analogue in terahertz hybrid metal-graphene metamaterials

Strong light-matter coupling manifested by Rabi splitting has attracted tremendous attention due to its fundamental importance in cavity quantum-electrodynamics research and great potentials in quantum information applications. A prerequisite for practical applications of the strong coupling in future optoelectronic devices is an all-solid-state system exhibiting room-temperature Rabi splitting with active control. Here we realized such a system in heterostructure consisted of monolayer WS2 and an individual plasmonic gold nanorod. By taking advantages of the small mode volume of the nanorod and large transition dipole moment of the WS2 exciton, giant Rabi splitting energies of 91-133 meV can be achieved at ambient conditions, which only involve a small number of excitons. The strong light-matter coupling can be dynamically tuned either by electrostatic gating or temperature scanning. These findings can pave the way toward active nanophotonic devices operating at room temperature.

Room-Temperature Strong Light–Matter Interaction with Active Control in Single Plasmonic Nanorod Coupled with Two-Dimensional Atomic Crystals

Reaching the quantum optics limit of strong light-matter interactions between a single exciton and a plasmon mode is highly desirable, because it opens up possibilities to explore room-temperature quantum devices operating at the single-photon level. However, two challenges severely hinder the realization of this limit: the integration of single-exciton emitters with plasmonic nanostructures and making the coupling strength at the single-exciton level overcome the large damping of the plasmon mode. Here, we demonstrate that these two hindrances can be overcome by attaching individual $J$ aggregates to single cuboid Au@Ag nanorods. In such hybrid nanosystems, both the ultrasmall mode volume of $\ensuremath{\sim}71\text{ }\text{ }{\mathrm{nm}}^{3}$ and the ultrashort interaction distance of less than 0.9 nm make the coupling coefficient between a single $J$-aggregate exciton and the cuboid nanorod as high as $\ensuremath{\sim}41.6\text{ }\text{ }\mathrm{meV}$, enabling strong light-matter interactions to be achieved at the quantum optics limit in single open plasmonic nanocavities.

Strong Light-Matter Interactions in Single Open Plasmonic Nanocavities at the Quantum Optics Limit.

Fano resonance arising from the interaction between a broad “bright” mode and a narrow “dark” mode has been widely investigated in symmetry-breaking structures made of noble metals such as plasmonic asymmetric oligomers or other well-designed nanostructures. However, Fano resonance in nanoscale all-dielectric dimers has not been experimentally demonstrated so far. We report the first experimental observation of directional Fano resonance in silicon nanosphere dimers (both homodimer and heterodimer) and clarify that the coupling between magnetic and electric dipole modes can easily generate Fano resonance in all-dielectric oligomers, distinctly differing from conventional Fano resonances based on electric responses or artificial optical magnetism. A silicon nanosphere dimer, exhibiting a strong magnetic response inside and an electric enhancement in the gap, is an excellent structure to support magnetic-based Fano scattering. Interactions between magnetic and electric dipoles can suppress backward scatteri...

Directional Fano Resonance in a Silicon Nanosphere Dimer

The solar-driven transformation of alcohols into hydrogen and value-added products is a promising strategy for the green synthesis of fuels and fine chemicals. However, achieving these reactions via photocatalysts with efficient photo-adsorption and charge‑separation is challenging. Herein, a novel all-solid-state Z‑scheme catalyst was constructed. In this system, ZnIn2S4 nanosheets were grown in situ on the surfaces of CeO2 nanorods. Such 2D/1D composites showing intimate contact can form solid Z-scheme heterostructures that combine the excellent visible-light absorption of ZnIn2S4 nanosheets, and the fast charge transport of CeO2 nanorods, while retaining the strong reducibility of electrons in the CB of ZnIn2S4 nanosheets and the oxidizability of holes in the VB of CeO2 nanorods. These synergistic advantages enhanced the photocatalytic performance, and the benzaldehyde and hydrogen yields reached 664.1 and 1496.6 μmol gcat−1. h−1 respectively. Moreover, a high benzaldehyde selectivity was achieved. These findings provide new opportunities for application of hierarchical Z-scheme metal-oxide-based photocatalysts.

All solid-state Z‑scheme CeO2/ZnIn2S4 hybrid for the photocatalytic selective oxidation of aromatic alcohols coupled with hydrogen evolution

Electromagnetically induced transparency is a type of quantum interference that induces near-zero reflection and near-perfect transmission. As a classical analogy, metal nanostructure plasmonic 'molecules' produce plasmon-induced transparency conventionally. Herein, an electromagnetically induced transparency interaction is demonstrated in silicon nanosphere oligomers, wherein the strong magnetic resonance couples with the electric gap mode effectively to markedly suppress reflection. As a result, a narrow-band transparency window created at visible wavelengths, called magnetically induced transparency, is easily realized in nearly touching silicon nanospheres, exhibiting low dependence on the number of spheres and aggregate states compared with plasmon induced transparency. A hybridization mechanism between magnetic and electric modes is proposed to pursue the physical origin, which is crucial to build all-dielectric metamaterials. Remarkably, magnetic induced transparency effect exhibiting near-zero reflection and near-perfect transmission causes light to propagate with no extra phase change. This makes silicon nanosphere oligomers promising as a unit cell in epsilon-near-zero metamaterials.

/pdf/magnetically-induced-forward-scattering-at-visible-1khzoyd02k.pdf

Hao Wang

Papers

Room-Temperature Strong Light–Matter Interaction with Active Control in Single Plasmonic Nanorod Coupled with Two-Dimensional Atomic Crystals

Strong Light-Matter Interactions in Single Open Plasmonic Nanocavities at the Quantum Optics Limit.

Directional Fano Resonance in a Silicon Nanosphere Dimer

All solid-state Z‑scheme CeO2/ZnIn2S4 hybrid for the photocatalytic selective oxidation of aromatic alcohols coupled with hydrogen evolution

Magnetically induced forward scattering at visible wavelengths in silicon nanosphere oligomers