Plasmonics for improved photovoltaic devices

Spectrally Engineered Coatings for Steering the Solar Photons

The spectral properties of radiative cooling (RC) and photovoltaic (PV) govern their capacity to utilize solar photons at distinct energy levels. However, spectral mismatches with the solar spectrum result in significant inefficiencies: non-photovoltaic heat losses in PV panels and wasted energy from reflected solar radiation in RC systems. To address this, a photoluminescent RC coating with spectrally selective reflectivity is developed to be integrated it with bifacial photovoltaic (biPV) panels. The high reflectivity of the RC coating directs photons to the rear side of the PV panels, while its spectral selectivity optimizes the energy distribution of photons reaching the rear side, resulting in a 32% increase in the overall power output of the bifacial PV system. Additionally, the incorporation of photoluminescent materials enables the conversion of absorbed photons into luminescence rather than heat by suppressing non-radiative transitions. This reduces effective solar absorption by 14% and enhances radiative cooling performance. Simulated urban rooftop deployment demonstrates that this dual-harvesting system meet ≈18.1% of Hong Kong's annual electricity demand, offering a scalable pathway toward carbon-neutral cities.

Permanent Dipole Moment in a Quantum-Confined Two-Dimensional Metal Revealed by Electric Double Layer Gating

The tunable optical properties of metals through size-dependent quantum effects have attracted attention due to synthesis of chemically stable, ultrathin, and two-dimensional metals. Gate tunability, from the reduced screening of low-dimensional metals, adds an additional route for control over optical properties. Here, two-dimensional (2D) Ga is synthesized via confinement heteroepitaxy and patterned into electric-double-layer (EDL) gated transistors. 2D Ga is predicted to have an out-of-plane permanent dipole moment resulting from a non-centrosymmetric interface. Alternating current EDL gating induces a measurable change in 2D Ga reflectivity of ΔR/R ∼ 8 × 10-4. The optical response is dominated by a linear Stark shift of 1.8 meV, corresponding to a 0.4 D change in the permanent dipole moment between the ground and excited states of 2D Ga. These results are the first demonstration of 2D metal gating and the first direct evidence of a permanent dipole moment in a 2D metal.

Optimizing the Shell Thickness of Ag@TiO2 Nanostructures by a Simple Top-Down Method to Engineer Effective SERS Substrates and Photocatalysts

In this article, we discuss a simple method to prepare core-shell Ag@TiO2 nanoparticles (NPs) with an optimized shell thickness to engineer plasmonic photocatalysts and surface-enhanced Raman scattering (SERS) substrates. Variation in the shell (TiO2) thickness was analyzed by an acid-etching method, and the deterioration of the shell was traced by monitoring the extinction spectra of both colloidal and solid-supported Ag@TiO2 NPs. Attainment of the optimum shell thickness was confirmed by noticing the simultaneous appearance of the LSPR absorption band (at 450 nm) of core silver nanostructures (d = ∼10 nm) and the scattering signature of the shell (TiO2) in the extinction spectrum of Ag@TiO2 NPs. This study showed that the optimum thickness of TiO2 is ∼2 nm, which allowed LSPR excitation by visible light. The observed blue shift of the LSPR peak, compared to the unetched Ag@TiO2 NPs, with etching time indicated the size reduction of the NPs. Ag@TiO2 with the optimum thickness exhibited a reaction rate five times faster than that of unetched Ag@TiO2 under visible light irradiation. Ag@TiO2 NPs exhibited higher photocatalytic activity under visible light irradiation than under UV light. Furthermore, Ag@TiO2 NPs with the optimized thickness exhibited significantly higher SERS activity than the unetched Ag@TiO2 NPs. The elevated photocatalytic and SERS activities exhibited by engineered Ag@TiO2 NPs reveal the effectiveness of the etching process in creating a plasmonic effect in core(plasmonic)-shell (semiconductor) nanostructures.

Hollow silver nanoparticle formation under ultrafast laser irradiation via single- and multiple-shots

The morphological changes induced in metal nanoparticles by the interaction with laser pulses have an important impact on their optical response. In this work, by means of an atomistic model, we have studied the formation of cavities in spherical silver nanoparticles embedded in amorphous silica using one or more femtosecond laser pulses. The model allows us to identify the different processes that lead to cavity formation and how they affect the variation of the aspect ratio, i.e., the relationship between the size of the cavity and that of the metallic sphere. The model is used to explain experiments revealing the conditions necessary to produce hollow metal nanoparticles. New information on hollow nanoparticle formation both in single shot and multiple shot regimes is reported. The atomistic model in combination with an optical model constitutes a tool to tune the properties of hollow nanoparticles, as shown in this paper. This way, we can achieve a fine control over the aspect ratio and, thus, about the localized surface plasmon resonance of the hollow nanoparticles.

A dynamic broadband plasmonic absorber enabled by electrochemical lithium metal batteries

As plasmonic absorbers attract considerable attention in the fields of solar energy harvesting, sensors, and cloaking technology, achieving dynamic tuning holds promise for multifunctional applications. However, existing designs face challenges in achieving real-time dynamic regulation across the visible band. In this study, we propose an innovative approach to achieve dynamic broadband absorption at visible wavelengths via an electrochemical lithium metal battery. Through rigorous experimentation and simulation, we demonstrate that the dynamic absorber achieves remarkable reversibility, with 80% absorption at lithium deposition states and a 40% modulation amplitude in reflectance over 30 cycles. At the intersection of the plasmonic absorber and lithium battery, our results may provide insights for light detection such as the monitoring environment.

Nanofabrication for Nanophotonics

Nanofabrication, a pivotal technology at the intersection of nanoscale engineering and high-resolution patterning, has substantially advanced over recent decades. This technology enables the creation of nanopatterns on substrates crucial for developing nanophotonic devices and other applications in diverse fields including electronics and biosciences. Here, this mega-review comprehensively explores various facets of nanofabrication focusing on its application in nanophotonics. It delves into high-resolution techniques like focused ion beam and electron beam lithography, methods for 3D complex structure fabrication, scalable manufacturing approaches, and material compatibility considerations. Special attention is given to emerging trends such as the utilization of two-photon lithography for 3D structures and advanced materials like phase change substances and 2D materials with excitonic properties. By highlighting these advancements, the review aims to provide insights into the ongoing evolution of nanofabrication, encouraging further research and application in creating functional nanostructures. This work encapsulates critical developments and future perspectives, offering a detailed narrative on the state-of-the-art in nanofabrication tailored for both new researchers and seasoned experts in the field.

Interface-Tailored Secondary Excitation and Ultrafast Charge/Energy Transfer in Ti3C2Tx-MoS2 Heterostructure Films

Charge/energy separation across interfaces of plasmonic materials is vital for minimizing plasmonic losses and enhancing their performance in photochemical and optoelectronic applications. While heterostructures combining plasmonic two-dimensional transition metal carbides/nitrides (MXenes) and semiconducting transition metal dichalcogenides (TMDs) hold significant potential, the mechanisms governing plasmon-induced carrier dynamics at these interfaces remain elusive. Here, we uncover a distinctive secondary excitation phenomenon and an ultrafast charge/energy transfer process in heterostructure films composed of macro-scale Ti3C2Tx and MoS2 films. Using Rayleigh-Bénard convection and Marangoni effect-induced self-assembly, we fabricate large-scale (square centimeters) Ti3C2Tx and MoS2 films composed of edge-connected monolayer nanoflakes. These films are flexibly stacked in a controlled sequence to form macroscopic heterostructures, enabling the investigation and manipulation of excited-state dynamics using transient absorption and optical pump-terahertz probe spectroscopy. In the Ti3C2Tx-MoS2 heterostructure, we observe a secondary excitation in MoS2 driven by the surface plasmon resonance of Ti3C2Tx. This phenomenon, with a characteristic rise time constant of ∼70 ps, is likely facilitated by acoustic phonon recycling across the interface. Further interfacial thermal transport engineering─achieved by tailoring the sequence and combination of interfaces in trilayer heterostructures─allows extending the characteristic time to ∼175 ps. Furthermore, we identify a sub-150 fs ultrafast charge/energy transfer process from Ti3C2Tx to MoS2. The transfer efficiency is strongly dependent on the excitation photon energy, resulting in amplified photoconductivity in MoS2 by up to ∼180% under 3.10 eV excitation. These insights are crucial for developing plasmonic MXene-based heterostructures, paving the way for advancements in photochemical and optoelectronic applications.

Chemical Interface Damping Revealed by Single-Particle Absorption Spectroscopy

Plasmon-induced interfacial charge separation is a promising way to efficiently extract energetic carriers through direct plasmon decay. This mechanism of charge transfer has been investigated by single-particle scattering spectroscopy, which measures the homogeneous plasmon line width. The line width is broadened by charge transfer, generally known as chemical interface damping. However, conflicting reports exist regarding the effect of chemical interface damping on the corresponding single-particle absorption spectrum, which is needed to accurately determine absolute light conversion efficiencies. This work aims to resolve this question by directly correlating absorption and scattering spectra of individual gold nanorods in the presence and absence of a charge-accepting interface. We find that for TiO2 coated nanorods, the absorption line width is indeed broadened due to chemical interface damping but is overall narrower than the scattering line width. Chemical interface damping is furthermore found to increase with larger resonance energies. The observed differences in line widths between absorption and scattering are elucidated within the context of an analytically tractable model describing the lowest energy optically bright and higher-order optically dark plasmon modes of the nanorod, including bulk, radiative, and chemical interface damping effects. Taken together, these results establish that single-particle absorption spectroscopy is capable of revealing interfacial charge injection by direct plasmon decay.

Ultraviolet narrowband all-dielectric metasurface absorber with an ultra-thin absorption layer

Ultraviolet (UV, 200-400 nm) detection with high efficiency and excellent spectral resolution is essential in spectral analysis. This Letter proposes a UV narrowband all-dielectric metasurface absorber with an ultra-thin absorption layer. The design incorporates lossless Al2O3 resonators placed on a thin (20 nm) lossy Ga2O3 film, which enhances the absorption intensity at a specific wavelength. The near-perfect narrowband absorption enhancement results from the spectral overlap of the magnetic dipole (MD) and the electric dipole (ED) absorption modes by surface lattice resonance (SLR). The proposed absorber exhibits high-efficiency and high-quality (Q) absorption performance (A > 95%, Q ∼ 231) and allows for flexible control over the absorption wavelength through simple parameter adjustments. These features make it ideal for narrowband emission, spectrum detection, and multispectral sensing.

The dynamics of plasmon-induced hot carrier creation in colloidal gold

The generation and dynamics of plasmon-induced hot carriers in gold nanoparticles offer crucial insights into nonequilibrium states for energy applications, yet the underlying mechanisms remain experimentally elusive. Here, we leverage ultrafast X-ray absorption spectroscopy (XAS) to directly capture hot carrier dynamics with sub-50 fs temporal resolution, providing clear evidence of plasmon decay mechanisms. We observe the sequential processes of Landau damping (~25 fs) and hot carrier thermalization (~1.5 ps), identifying hot carrier formation as a significant decay pathway. Energy distribution measurements reveal carriers in non-Fermi-Dirac states persisting beyond 500 fs and observe electron populations exceeding single-photon excitation energy, indicating the role of an Auger heating mechanism alongside traditional impact excitation. These findings deepen the understanding of hot carrier behavior under localized surface plasmon resonance, offering valuable implications for applications in photocatalysis, photovoltaics, and phototherapy. This work establishes a methodological framework for studying hot carrier dynamics, opening avenues for optimizing energy transfer processes in nanoscale plasmonic systems.

Emission Enhancement of ZnO Thin Films in Ultraviolet Wavelength Region Using Au Nano-Hemisphere on Al Mirror Structures

Using a heterogeneous metal Nano Hemisphere on Mirror (NHoM) structure, composed of an Al2O3 thin film and Au nano-hemispheres formed on a thick Al film, we successfully generated two distinct surface plasmon resonance (SPR) peaks: one in the ultraviolet (UV) wavelength range below 400 nm and another in the visible range between 600 and 700 nm. This NHoM structure can be fabricated through a straightforward process involving deposition, sputtering, and annealing, enabling rapid, large-area formation. By adjusting the thickness of the Al2O3 spacer layer in the NHoM structure, we precisely controlled the localized surface plasmon resonance (LSPR) wavelength, spanning a wide range from the UV to the visible spectrum. Through this tuning, we enhanced the band-edge UV emission of the ZnO thin film by a factor of 35. Temperature-dependent measurements of emission intensity revealed that the NHoM structure increased the internal quantum efficiency (IQE) of the ZnO thin film from 8% to 19%. The heterometallic NHoM structure proposed in this study enables wide-ranging control of SPR wavelengths and demonstrates significant potential for applications in enhancing luminescence in the deep ultraviolet (DUV) region, where luminescence efficiency is typically low.

Efficient Size-Dependent Hot Electron Transfer from Au to TiO2 Nanoparticles

Harvesting of plasmon-induced hot carriers at the metal/semiconductor interface offers a promising and innovative avenue for solar energy conversion. However, their practical implementation is often hampered by their limited efficiencies. Herein, we have demonstrated a highly efficient plasmonic hot electron transfer with a quantum efficiency (QE) of up to 57 ± 4% from 5.25 nm Au nanoparticles (NPs) to TiO2 films under 400 nm ultrafast laser excitation. The observed hot electron transfer QEs decrease at larger particle sizes, to 20% for 9.1 nm Au, and show negligible changes with excitation wavelengths at 400, 500, and 600 nm. Analysis of the size and excitation wavelength dependent hot electron transfer QEs suggests they contain contributions of interband absorption, indirect plasmon-induced hot electron transfer (PHET), and direct plasmon-induced interfacial charge transfer transition (PICTT) pathways, and QEs of all three pathways increase at smaller Au size. Our result suggests that reducing plasmon particle sizes is a promising approach for efficient plasmonic hot-carrier extraction.

Flexible Multilayer Plasmonic Films for Biosensing and Photoemitting Applications

Flexible plasmon metasensor devices describe the use of multiple Ag/Al2O3/mica layers for tunable plasmonic resonances and are a promising research direction. Here, we report on a flexible Ag/Al2O3/mica multilayer platform and its excellent performance on flexible biosensors and photon-emitting devices. In our approach, muscovite (mica) was adopted as a single-crystal substrate due to its optical transparency and mechanical flexibility. The Ag/Al2O3/mica multilayer film is characterized by X-ray diffraction and transmission electron microscopy. Optical, plasmonic, and biosensing studies of Ag/Al2O3/mica multilayers are performed for detailed understanding. A combination of optical absorption, numerical simulations, and optical reflectance measurements has confirmed the biosensor performance. Two kinds of flexible plasmonic device applications are reported here, including (1) plasmonic biosensors with high refractive index sensitivities and (2) significantly enhanced spontaneous photoluminescence (PL) of monolayer tungsten disulfide (WS2) spectra. We found that the PL emission under 0.4 mm-1 curvature bending state increased to 16% compared to the unbent state and redshift of 60 meV/% strain in the emission of WS2 monolayer. Furthermore, the Ag/Al2O3/mica multilayer film displays robust stability and strong endurance up to a bending curvature of 0.4 mm-1. This study shows great potential to be used for biosensors and flexible optoelectronics.

Photoabsorption of silver cluster cations in an ion trap: nonlinear action spectra via multi-photon dissociation vs. directly measured linear absorption spectra

We report photodissociation processes and spectral measurements upon photoabsorption of size-selected cationic silver clusters, AgN+, stored in an ion trap. The experiment shows that small clusters (N ≲ 15) dissociate upon one-photon absorption, whereas larger ones require multiple photons up to five in the present study. The emergence of multi-photon processes is attributed to collisional cooling in the presence of a buffer helium gas in the trap, which competes with size-dependent dissociation rates. These observations are explained by simulations that consider the two competing effects, where the statistical Rice-Ramsperger-Kassel (RRK) theory is employed to evaluate dissociation rates. Action spectra of photodissociation are compared with linear absorption spectra directly measured by cavity-ring-down-type high-sensitivity spectroscopy, revealing that the profiles of the action spectra are sharpened by the nonlinear effects in the multi-photon regime. This observation demonstrates the importance of the linear absorption measurement to obtain both spectral profiles and cross sections for large clusters that exhibit multi-photon dissociation.

Enhanced coupling of perovskites with semiconductive properties by tuning multi-modal optically active nanostructured set-ups for photonics, photovoltaics and energy applications

This review describes the coupling of semiconducting materials with perovskites as main optically active elements for enhancing the performance depending on the optical set-up and coupling phenomena. The various uses of semiconductor nanoparticles and related nanomaterials for energy conduction and harvesting are discussed. Thus, it was obtained different materials highlighting the properties of perovskites incorporated within heterojunctions and hybrid nanomaterials where varied materials and sources were joined. Different multi-layered substrates are reported, and different strategies for improved electron and energy transfer and harvesting are elucidated Further, enhanced coupling of semiconductive properties for the above-mentioned processes is discussed. In this regard, various nanomaterials and their properties for improving energy applications such as solar cells are demonstrated. Moreover, the incorporation of plasmonic properties from different noble metal sources and pseudo-electromagnetic properties from graphene and carbon allotropes is discussed. Since variations in electromagnetic fields affect the semiconductive properties, it leads to varying effects and potential applications within the energy research field. Hence, this review could guide the development within energy research fields as nanophotonics, photovoltaics, and energy. This review is mainly focused on the development of solar energy cells by incorporating perovskites with varied hybrid nanomaterials, photonic materials, and metamaterials.

Polarization Spin Inversion with Nonlinear Plasmon Scattering

We report on circularly polarized Gaussian beam spin angular momenta that can be inverted upon scattering with quadrupole plasmon modes. The conditions for such conversion are met with high-angle collection, dark-field scattering microscopy on spherical plasmonic particles. We further report that silvered nanoporous silica microparticles exhibit a strong nonlinearity in their scattering, specifically a reverse saturated scattering (RSS), when exposed to high laser power densities on the sample of ca. 5 GW/cm2. Handedness conversion by these microparticles is only observed at wavelengths tuned to the quadrupole modes. Conversely, the scattering remains linear, and the handedness is unchanged, when the same particles are illuminated with low laser power densities of ca. 10 W/cm2. We infer that RSS tuned to the quadrupole modes sufficiently enhances their contribution so that they dominate the high-angle scattering, thereby justifying the light spin inversion. Moreover, the addition of a self-assembled monolayer of ethynylaniline (EA) on the microparticles results in handedness conversion for both low and high incident power, as expected from preferable dipole damping and plasmon mode red shift. This demonstrates that optical nonlinearity in scattering can be exploited for polarization tuning in plasmonic metamaterials.

Plasmon hybridization model in molecules: molecular jackhammers

We recently demonstrated molecular plasmons in cyanine dyes for the conversion of photon energy into mechanical energy through a whole-molecule coherent vibronic-driven-action. Here we present a model, a molecular plasmon analogue of molecular orbital theory and of plasmon hybridization in metal nanostructures. This model describes that molecular plasmons can be obtained from the combination or hybridization of elementary molecular fragments, resulting in molecules with hybridized plasmon resonances in the electromagnetic spectrum. We applied our approach to the hybridization of the benzoindole and heptamethine fragments for understanding of the resonance frequencies in cyanines using UV-vis and Raman spectroscopy. The molecular plasmon resonances in cyanines are tunable by engineering molecular structure modifications and controlling the dielectric constant of the medium in which the cyanines are dissolved. We measured the plasmonicity index, an easy-to-use and powerful tool to predict and quantify if an organic molecule in solution is a molecular plasmon. This is done by analyzing the UV-vis spectrum as a function of the change of the dielectric constant of the solvent. Our model provides a tool for understanding how to manipulate chemical structures and their interaction with light at the molecular scale as plasmon-driven molecular jackhammers for applications at the interface with biological structures.

Development of an innovative reusable terahertz biosensor platform integrated graphene and all-silicon groove for detecting cancer cells in aqueous environments

The label-free detection and analysis of cancer cells using portable biosensing devices is crucial and promising. In this study, a novel reusable biosensing platform with a microfluidic-like based on terahertz plasmonic metasurfaces utilizing graphene integrated with an all-silicon groove for detecting liquid live cancer cells was developed. The proposed biosensor platform stands out because it can differentiate between the concentrations of three types of cancer cells by monitoring changes in resonance intensity and phase difference. The minimum concentration for identification was reduced to as low as 5 × 104 cells/mL. We effectively constructed two-dimensional optical intensity cards using continuous wavelet transforms, which presented a more accurate approach for the recognition and determination of the three types of cancer cells. Our proposed biosensors show great potential for the determination and recognition of label-free cancer cells in aqueous environments as alternatives to non-immune biosensing technology.

Hierarchically Promoted Light Harvesting and Management in Photothermal Solar Steam Generation

Solar steam generation (SSG) presents a promising approach to addressing the global water crisis. Central to SSG is solar photothermal conversion that requires efficient light harvesting and management. Hierarchical structures with multi-scale light management are therefore crucial for SSG. At the molecular and sub-nanoscale levels, materials are fine-tuned for broadband light absorption. Advancing to the nano- and microscale, structures are tailored to enhance light harvesting through internal reflections, scattering, and diverse confinement effects. At the macroscopic level, light capture is optimized through rationally designed device geometries, configurations, and arrangements of solar absorber materials. While the performance of SSG relies on various factors including heat transport, physicochemical interactions at the water/air and material/water interfaces, salt dynamics, etc., efficient light capture and utilization holds a predominant role because sunlight is the sole energy source. This review focuses on the critical, yet often underestimated, role of hierarchical light harvesting/management at different dimensional scales in SSG. By correlating light management with the structure-property relationships, the recent advances in SSG are discussed, shedding light on the current challenges and possible future trends and opportunities in this domain.

Enhanced multifaceted model for plasmon-driven Schottky solar cells with integrated thermal effects

This paper explores the development of an opto-thermal-electrical model for plasmonic Schottky solar cells (PSSCs) using a comprehensive multiphysics approach. We simulated the optical properties, power conversion efficiencies, and energy yield of PSSCs with varying nanoparticle (NP) configurations and sizes. Our spectral analysis focused on the absorption characteristics of these solar cells, examining systems sized 3 × 3, 5 × 5, and 7  × 7, with NP radii ranging from 10 to 150 nm. The study addresses a significant gap in solar cell research by presenting a novel multi-physics energy yield model for PSSCs decorated with gold nanoparticles (Au-NPs) on silicon absorbers. This integrated framework uniquely couples optical, electrical, and thermal responses for the prediction of global energy yield maps. Total spectral heat absorption was evaluated over a range of 300 nm to 1200 nm. This spectral heating was further deconvoluted into nanoparticle heating and thermalization heating in a silicon absorber. The findings indicated that the 5 × 5 NP array with a 70 nm radius enhances electrical performance, with the short-circuit current density (Jsc) reaching 11.54 mA/cm2-A 47% improvement compared to traditional bare silicon Schottky cells of 2 μm thickness. However, this electrical enhancement was also accompanied by a significant increase in heat generation within the nanoparticles, with thermal gains up to 182.5% relative to the bare silicon cells. This substantial rise in thermal energy highlights the critical need for advanced thermal management strategies to mitigate overheating and ensure the overall efficiency of plasmonic-enhanced solar cells. Enhanced energy yield maps confirm the model's predictions, showing improved outputs globally, especially in sunny regions with potential annual energy yield gains up to 80 kWh/m2.

Lignosulfonate as a versatile regulator for the mediated synthesis of Ag@AgCl nanocubes

The remarkable catalytic activity, optical properties, and electrochemical behavior of nanomaterials based on noble metals (NM) are profoundly influenced by their physical characteristics, including particle size, morphology, and crystal structure. Effective regulation of these parameters necessitates a refined methodology. Lignin, a natural aromatic compound abundant in hydroxyl, carbonyl, carboxyl, and sulfonic acid groups, has emerged as an eco-friendly surfactant, reducing agent, and dispersant, offering the potential to precisely control the particle size and morphology of NM-based nanomaterials. In this study, lignosulfonate (LS) was utilized as a versatile regulator efficient in the capacities of reduction, capping, and dispersal for the synthesis of Ag@AgCl nanocubes. LS concentration and reaction time were identified as crucial factors impacting the ultimate particle size and morphology of Ag@AgCl nanocubes. The Ag@AgCl nanocubes, with a particle size of 30 ± 10 nm, were successfully synthesized under the optimized conditions of a 1.0 mM LS concentration and a 1-hour reaction period. As a reducing agent, LS facilitates the conversion of silver ions originating from AgCl to silver nanoparticles, following an etching-like mechanism that yields AgCl seeds with a uniform cubic particle size. The obtained Ag@AgCl nanocubes exhibit a stable morphology and excellent dispersion characteristics.

Strain-Reduced Inversion Symmetry in Ultrathin SnP2Se6 Crystals for Giant Bulk Piezophotovoltaic Generation

With the potential to surpass the Shockley-Queisser (S-Q) limitation for solar energy conversion, the bulk photovoltaic (BPV) effect, which is induced by the broken inversion symmetry of the lattice, presents prospects for future light-harvesting technologies. However, the development of BPV is largely limited by the low solar spectrum conversion efficiency of existing noncentrosymmetric materials with wide band gaps. This study reports that the strain-induced reduction of inversion symmetry can enhance the second-order nonlinear susceptibility (χ(2)) of SnP2Se6 crystals by an order of magnitude, which contributes to an extremely high value of 1.3 × 10-8 m·V-1 under 1550 nm excitation, and is high among two-dimensional (2D) crystals. More importantly, owing to the orientation-dependent reduction of lattice symmetry, the BPV generation induced by strain, referred to as the bulk piezophotovoltaic effect, is demonstrated in the SnP2Se6 crystal with strong in-plane anisotropy. The strain along the Se zigzag direction greatly facilitates the generation of the giant photocurrent covering an extended spectrum ranging from 400 to 1100 nm, resulting in leading-level values of the BPV coefficient among noncentrosymmetric crystals, while the BPV effect is barely modulated along the Se armchair direction even with a large strain of 0.57%. This study highlights the potential of the bulk piezophotovoltaic effects for energy conversion efficiency and offers a promising strategy for the design of next-generation light-harvesting devices.

Plasmon Dynamics in Nanoclusters: Dephasing Revealed by Excited States Evaluation

The photocatalytic efficiency of materials such as graphene and noble metal nanoclusters depends on their plasmon lifetimes. Plasmon dephasing and decay in these materials is thought to occur on ultrafast time scales, ranging from a few femtoseconds to hundreds of femtoseconds and longer. Here we focus on understanding the dephasing and decay pathways of excited states in small lithium and silver clusters and in plasmonic states of the π-conjugated molecule anthracene, providing insights that are crucial for interpreting optical properties and photophysics. To do this, we study the time dependence of the electronic density matrix of these molecules using a new approach that expresses the density matrix in terms of TDDFT eigenstates (ESs) of the TDDFT Hamiltonian. This approach, which involves combining linear response time-dependent density functional theory (LR-TDDFT) and real-time time-dependent density functional theory (RT-TDDFT), leads to an analysis of the electron dynamics in terms of ESs, rather than individual molecular orbital (MO) transitions as has typically been done. This circumvents the complexities and subjective biases that traditional MO-based analysis provides. We find in an analysis of the induced dipole moment in these molecules that what had previously been considered to be energy relaxation is actually dephasing associated with the eigenstates that are stationary after the excitation pulse is turned off. We conclude that the ES-basis analysis has significant potential to advance understanding of the electron dynamics of plasmonic nanomaterials, aiding their optimization for photocatalytic and technological applications.

Machine learning assisted plasmonic metascreen for enhanced broadband absorption in ultra-thin silicon films

We propose and demonstrate a data-driven plasmonic metascreen that efficiently absorbs incident light over a wide spectral range in an ultra-thin silicon film. By embedding a double-nanoring silver array within a 20 nm ultrathin amorphous silicon (a-Si) layer, we achieve a significant enhancement of light absorption. This enhancement arises from the interaction between the resonant cavity modes and localized plasmonic modes, requiring precise tuning of plasmon resonances to match the absorption region of the silicon active layer. To facilitate the device design and improve light absorption without increasing the thickness of the active layer, we develop a deep learning framework, which learns to map from the absorption spectra to the design space. This inverse design strategy helps to tune the absorption for selective spectral functionalities. Our optimized design surpasses the bare silicon planar device, exhibiting a remarkable enhancement of over 100%. Experimental validation confirms the broadband enhancement of light absorption in the proposed configuration. The proposed metascreen absorber holds great potential for light harvesting applications and may be leveraged to improve the light conversion efficiency of ultra-thin silicon solar cells, photodetectors, and optical filters.

Gold-Mercury-Platinum Alloy for Light-Enhanced Electrochemical Detection of Hydrogen Peroxide

In this study, a simple and easy synthesis strategy to realize the modification of AuHgPt nanoalloy materials on the surface of ITO glass at room temperature is presented. Gold nanoparticles as templates were obtained by electrochemical deposition, mercury was introduced as an intermediate to form an amalgam, and then a galvanic replacement reaction was utilized to successfully prepare gold-mercury-platinum (AuHgPt) nanoalloys. The obtained alloys were characterized by scanning electron microscopy, UV-Vis spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction techniques. The electrochemical sensing performance of the AuHgPt-modified electrode for hydrogen peroxide was evaluated by cyclic voltammetry and chronoamperometry. Under light conditions, the AuHgPt-modified electrode exhibited a desirable current response in the detection of hydrogen peroxide due to the synergistic effect of the localized surface plasmon resonance effect inherent in gold nanoparticles, and this synergistic effect improved the sensitivity of hydrogen peroxide detection. Meanwhile, the AuHgPt-modified electrode also exhibited better stability and reproducibility, which makes the modified electrode have great potential for various applications in the field of electrochemical sensing.

Harnessing Radiation for Nanotechnology: A Comprehensive Review of Techniques, Innovations, and Application

Nanomaterial properties such as size, structure, and composition can be controlled by manipulating radiation, such as gamma rays, X-rays, and electron beams. This control allows scientists to create materials with desired properties that can be used in a wide range of applications, from electronics to medicine. This use of radiation for nanotechnology is revolutionizing the way we design and manufacture materials. Additionally, radiation-induced nanomaterials are more cost effective and energy efficient. This technology is also having a positive impact on the environment, as materials are being produced with fewer emissions, less energy, and less waste. This cutting-edge technology is opening up new possibilities and has become an attractive option for many industries, from medical advancements to energy storage. It is also helping to make the world a better place by reducing our carbon footprint and preserving natural resources. This review aims to meticulously point out the synthesis approach and highlights significant progress in generating radiation-induced nanomaterials with tunable and complex morphologies. This comprehensive review article is essential for researchers to design innovative materials for advancements in health care, electronics, energy storage, and environmental remediation.

Free-electron coupling to surface polaritons mediated by small scatterers

The ability of surface polaritons (SPs) to enhance and manipulate light fields down to deep-subwavelength length scales enables applications in optical sensing and nonlinear optics at the nanoscale. However, the wavelength mismatch between light and SPs prevents direct optical excitation of surface-bound modes, thereby limiting the widespread development of SP-based photonics. Free electrons are a natural choice to directly excite strongly confined SPs because they can supply field components of high momentum at designated positions with subnanometer precision. Here, we theoretically explore free-electron-SP coupling mediated by small scatterers and show that low-energy electrons can efficiently excite surface modes with a maximum probability reached at an optimum surface-scatterer distance. By aligning the electron beam with a periodic array of scatterers placed near a polariton-supporting interface, in-plane Smith-Purcell emission results in the excitation of surface modes along well-defined directions. Our results support using scattering elements to excite SPs with low-energy electrons.

Continuous spectral and coupling-strength encoding with dual-gradient metasurfaces

To control and enhance light-matter interactions at the nanoscale, two parameters are central: the spectral overlap between an optical cavity mode and the material's spectral features (for example, excitonic or molecular absorption lines), and the quality factor of the cavity. Controlling both parameters simultaneously would enable the investigation of systems with complex spectral features, such as multicomponent molecular mixtures or heterogeneous solid-state materials. So far, it has been possible only to sample a limited set of data points within this two-dimensional parameter space. Here we introduce a nanophotonic approach that can simultaneously and continuously encode the spectral and quality-factor parameter space within a compact spatial area. We use a dual-gradient metasurface design composed of a two-dimensional array of smoothly varying subwavelength nanoresonators, each supporting a unique mode based on symmetry-protected bound states in the continuum. This results in 27,500 distinct modes and a mode density approaching the theoretical upper limit for metasurfaces. By applying our platform to surface-enhanced molecular spectroscopy, we find that the optimal quality factor for maximum sensitivity depends on the amount of analyte, enabling effective molecular detection regardless of analyte concentration within a single dual-gradient metasurface. Our design provides a method to analyse the complete spectral and coupling-strength parameter space of complex material systems for applications such as photocatalysis, chemical sensing and entangled photon generation.

Optoelectronic metadevices

Metasurfaces have introduced new opportunities in photonic design by offering unprecedented, nanoscale control over optical wavefronts. These artificially structured layers have largely been used to passively manipulate the flow of light by controlling its phase, amplitude, and polarization. However, they can also dynamically modulate these quantities and manipulate fundamental light absorption and emission processes. These valuable traits can extend their application domain to chipscale optoelectronics and conceptually new optical sources, displays, spatial light modulators, photodetectors, solar cells, and imaging systems. New opportunities and challenges have also emerged in the materials and device integration with existing technologies. This Review aims to consolidate the current research landscape and provide perspectives on metasurface capabilities specific to optoelectronic devices, giving new direction to future research and development efforts in academia and industry.

Direct Three-Dimensional Observation of the Plasmonic Near-Fields of a Nanoparticle with Circular Dichroism

Characterizing the spatial distribution of the electromagnetic fields of a plasmonic nanoparticle is crucial for exploiting its strong light-matter interaction for optoelectronic and catalytic applications. However, observing the near-fields in three dimensions with a high spatial resolution is still challenging. To realize efficient three-dimensional (3D) nanoscale mapping of the plasmonic fields of nanoparticles with complex shapes, this work established autoencoder-embedded electron energy loss spectroscopy (EELS) tomography. A 432-symmetric chiral gold nanoparticle, a nanoparticle with a high optical dissymmetry factor, was analyzed to relate its geometrical features to its exotic optical properties. Our deep-learning-based feature extraction method discriminated plasmons with different energies in the EEL spectra of the nanoparticle in which signals from multiple plasmons were intermixed; this component was key for acceptable 3D visualization of each plasmonic field separately using EELS tomography. With this methodology, the electric field of the plasmon that induces far-field circular dichroism was observed in 3D. The field linked to this chiroptical property was strong along the swirling edges of the particle, as predicted by a numerical calculation. This study provides insight into the correlation between structural and optical chiralities through direct 3D observation of the plasmonic fields. Furthermore, the strategy of implementing an autoencoder for EELS tomography can be generalized to achieve competent 3D analysis of other features, including the optical properties of the dielectrics and chemical states.

Electron confinement-induced plasmonic breakdown in metals

Plasmon resonance represents the collective oscillation of free electron gas density and enables enhanced light-matter interactions in nanoscale dimensions. Traditionally, the classical Drude model describes plasmonic excitation, wherein plasma frequency exhibits no spatial dispersion. Here, we show conclusive experimental evidence of the breakdown of plasmon resonance and a consequent metal-insulator transition in an ultrathin refractory plasmonic material, hafnium nitride (HfN). Epitaxial HfN thick films exhibit a low-loss and high-quality Drude-like plasmon resonance in the visible spectral range. However, as the film thickness is reduced to nanoscale dimensions, Coulomb interaction among electrons increases because of electron confinement, leading to the spatial dispersion of plasma frequency. With a further decrease in thickness, electrons lose their ability to shield the incident electric field, turning the medium into a dielectric. The observed metal-insulator transition might carry some signatures of Wigner crystallization and indicates that such transdimensional, between 2D and 3D, films can serve as a promising playground to study strongly correlated electron systems.

Using Thermal Crowding to Direct Pattern Formation on the Nanoscale

Metal films and other metal geometries of nanoscale thickness deposited on an insulating substrate, when exposed to laser irradiation, melt and evolve as fluids as long as their temperature is sufficiently high. This evolution often leads to pattern formation, which may be influenced strongly by material parameters that are temperature dependent. In addition, the laser heat absorption itself depends on the time-dependent metal thickness. Self-consistent modeling of evolving metal films shows that, by controlling the amount and geometry of the deposited metal, one can control the instability development. In particular, we demonstrate the "thermal crowding" effect: additional metal leads to elevated temperatures, which strongly influence the metal evolution, even if the metal geometries are disjoint. We demonstrate that the communication of disjoint metal domains occurs via heat diffusion through the underlying substrate. Fully self-consistent modeling focusing on the dominant effects, as well as accurate time-dependent simulations, allow us to describe the main features of thermal crowding and provide a route to control fluid instabilities and pattern formation on the nanoscale.

Hot carrier transfer from plasmon decay in Ag20at H-Si(111) surface: real-time TDDFT simulation in Wannier gauge

Plasmon decay is believed to play an essential role in inducing hot carrier transfer at the interfaces between plasmonic nanoparticles and semiconductor surfaces. In this work, we employ real-time time-dependent density functional theory (RT-TDDFT) simulation in the Wannier gauge to gain quantum-mechanical insights into the nonlinear dynamics of the plasmon decay in the Ag20nanoparticle at a semiconductor surface. The first-principles simulations show that the plasmon decay is more than two times faster when the Ag20nanoparticle is adsorbed on a hydrogen-terminated Si(111) surface, taking place within 100 femtoseconds of the plasmon excitation. Hot carrier transfer across the interface is observed as the plasmon decay takes place, and nearly 30% of holes are generated deep in the valence band of the semiconductor surface. The use of Wannier gauge in RT-TDDFT simulation is particularly convenient for gaining quantum-mechanical insights into non-equilibrium electron dynamics in complex heterogeneous systems.

Enhanced efficiency of carbon based all perovskite tandem solar cells via cubic plasmonic metallic nanoparticles with dielectric nano shells

This study investigates a carbon-based all-perovskite tandem solar cell (AP-TSC) with the structure ITO, SnO₂, Cs₀.₂FA₀.₈Pb(I₀.₇Br₀.₃)₃, WS₂, MoO₃, ITO, C₆₀, MAPb₀.₅Sn₀.₅I₃, PEDOT: PSS, Carbon. The bandgap configuration of the cell is 1.75 eV/1.17 eV, which is theoretically limited to 36% efficiency. The effectiveness of embedding cubic plasmonic metallic nanoparticles (NPs) made of Gold (Au) and Silver (Ag) within the absorber layers to eliminate the requirement for thicker absorber layers, decrease manufacturing costs and Pb toxicity is demonstrated in our analysis. This analysis was conducted using 3D Finite Element Method (FEM) simulations for both optical and electrical calculations. Prior to delving into the primary investigation of the tandem structure, a validation simulation was conducted to demonstrate the accuracy and reliability of the simulations. Notably, the efficiency mismatch observed during the validation simulation, specifically in relation to the incorporation of metallic nanoparticles (NPs), amounted to a mere 0.01%. To mitigate the potential issues of direct contact between metallic NPs and perovskite materials, such as increased thermal and chemical instability and recombination at the NP surface, a 5 nm dielectric shell was applied to the NPs. The incorporation of cubic core-shell Ag NPs resulted in a 15.32% enhancement in short-circuit current density, from 16.39 mA/cm² to 18.90 mA/cm², and a 15.68% increase in overall efficiency, from 26.9 to 31.12%. This research paves the way for the integration of core-shell metallic NPs in AP-TSCs, highlighting a significant potential for efficiency and stability improvements. In a dedicated section the band alignment of the sub-cell was addressed. Additionally, a thermal investigation of the proposed tandem structure was conducted, demonstrating the robustness of the proposed AP-TSC. Finally, the sensitivity analyses related to input parameters and the challenges associated with large-scale fabrication of the proposed AP-TSC were extensively discussed.

Discovery of Electromagnetic Surface Waves at the Interface between Perfect Electric Conductor and Perfect Magnetic Conductor Parallel-Plate Waveguides

We propose new electromagnetic surface waves at the interface formed by connecting perfect electric conductor (PEC) and perfect magnetic conductor (PMC) parallel plate waveguides containing materials with positive permittivities and permeabilities. This challenges the conventional understanding that surface waves require materials with negative permittivity or permeability. Theoretical mode analysis and numerical simulations have confirmed the existence of surface waves at the PEC-PMC interface. Additionally, a simulated prism coupling experiment validated the excitation of the surface watpdel 1ve at the PEC-PMC interface. The resonant response of the localized surface waves on the enclosed PEC-PMC surface of a cylinder also closely resembles that of a Drude cylinder. Our finding broadens the understanding of the conditions for generating electromagnetic surface waves and deepens our comprehension of electromagnetic phenomena.

Doubling Power Conversion Efficiency of Si Solar Cells

Improving solar cells' power conversion efficiency (PCE) is crucial to further the deployment of renewable electricity. In addition, solar cells cannot function at exceedingly low temperatures owing to the carrier freeze-out phenomenon. This report demonstrates that through temperature regulation, the PCE of monocrystalline single-junction silicon solar cells can be doubled to 50-60% under monochromatic lasers and the full spectrum of AM 1.5 light at low temperatures of 30-50 K by inhibiting the lattice atoms' thermal oscillations for suppressing thermal loss, an inherent feature of monocrystalline Si cells. Moreover, the light penetration, determined by its wavelength, plays a critical role in alleviating the carrier freeze-out effect and broadening the operational temperature range of silicon cells to temperatures as low as 10 K. Understanding these new observations opens tremendous opportunities for designing solar cells with even higher PCE to provide efficient and powerful energy sources for cryogenic devices and outer and deep space explorations.

Plasmonics Meets Perovskite Photovoltaics: Innovations and Challenges in Boosting Efficiency

Perovskite solar cells (PSCs) have garnered immense attention in recent years due to their outstanding optoelectronic properties and cost-effective fabrication methods, establishing them as promising candidates for next-generation photovoltaic technologies. Among the diverse strategies aimed at enhancing the power conversion efficiency (PCE) of PSCs, the incorporation of plasmonic nanoparticles has emerged as a pioneering approach. This review summarizes the latest research advancements in the utilization of plasmonic nanoparticles to enhance the performance of PSCs. We delve into the fundamental principles of plasmonic resonance and its interaction with perovskite materials, highlighting how localized surface plasmons can effectively broaden light absorption, facilitate hot-electron transfer (HET), and optimize charge separation dynamics. Recent strategies, including the design of tailored metal nanoparticles (MNPs), gratings, and hybrid plasmonic-photonic architectures, are critically evaluated for their efficacy in enhancing light trapping, increasing photocurrent, and mitigating charge recombination. Additionally, this review addresses the challenges associated with the integration of plasmonic elements into PSCs, including issues of scalability, compatibility, and cost-effectiveness. Finally, the review provides insights into future research directions aimed at advancing the field, thereby paving the way for next-generation, high-performance perovskite-based photovoltaic technologies.

Laser-synthesized plasmonic HfN-based nanoparticles as a novel multifunctional agent for photothermal therapy

Hafnium nitride nanoparticles (HfN NPs) can offer appealing plasmonic properties at the nanoscale, but the fabrication of stable water-dispersible solutions of non-toxic HfN NPs exhibiting plasmonic features in the window of relative biological transparency presents a great challenge. Here, we demonstrate a solution to this problem by employing ultrashort (femtosecond) laser ablation from a HfN target in organic solutions, followed by a coating of the formed NPs with polyethylene glycol (PEG) and subsequent dispersion in water. We show that the fabricated NPs exhibit plasmonic absorption bands with maxima around 590 nm, 620 nm, and 650 nm, depending on the synthesis environment (ethanol, acetone, and acetonitrile, respectively), which are largely red-shifted compared to what is expected from pure HfN NPs. The observed shift is explained by including nitrogen-deficient hafnium nitride and hafnium oxynitride phases inside the core and oxynitride coating of NPs, as follows from a series of structural characterization studies. We then show that the NPs can provide a strong photothermal effect under 808 nm excitation with a photothermal conversion coefficient of about 62%, which is comparable to the best values reported for plasmonic NPs. MTT and clonogenic assays evidenced very low cytotoxicity of PEG-coated HfN NPs to cancer cells from different tissues up to 100 μg mL-1 concentrations. We finally report a strong photothermal therapeutic effect of HfN NPs, as shown by 100% cell death under 808 nm light irradiation at NP concentrations lower than 25 μg mL-1. Combined with additional X-ray theranostic functionalities (CT scan and photon capture therapy) profiting from the high atomic number (Z = 72) of Hf, plasmonic HfN NPs promise the development of synergetically enhanced modalities for cancer treatment.

Using TiO2 to capture hot electrons for self-powered position-sensitive photodetection

As environmental issues arise, the demand for self-powered position-sensitive detectors (PSDs) is increasing because of their advantages in miniaturization and low power consumption. Finding higher efficiency schemes for energy conversion is paramount for realizing high-performance self-powered PSDs. Here, a surface plasmon-based approach was used to improve the energy conversion efficiency, and a plasmon-enhanced lateral photovoltaic effect (LPE) was observed in PSD with TiO2/Au nanorods (NRs)/Si structure. The Au NRs convert absorbed light energy into electricity by generating hot electrons, which are efficiently captured by the TiO2 layer, and the PSD is capable of generating position sensitivity as high as 251.75 mV/mm when illuminated by a 780 nm laser without any external power supply, i.e. about five times higher than similar sensors in previous studies. In addition, the position sensitivity can be tailored by the thickness of TiO2 films. The enhancement mechanism is investigated by a localized surface plasmon (LSP)-driven carrier diffusion model. These findings reveal an important strategy for high sensitivity and low energy cost PSDs while opening up new avenues for energy harvesting self-powered position sensors.

Thickness-dependent optical properties of low-loss transdimensional plasmonic Sr0.82NbO3 thin films

To develop alternative plasmonic materials for nanophotonic applications, the thickness-dependent optical properties of ultrathin plasmonic Sr0.82NbO3 (SNO) films deposited on MgO are investigated. As the thickness decreases from 10 to 2 nm, the film exhibits less metallic, epsilon-near-zero (ENZ) wavelength redshift and higher optical loss due to increased scattering. Nevertheless, the thinnest film still has a high carrier concentration of 1022 cm-3, and the real part of the dielectric functions of all films is less than zero in the near-infrared (NIR) wavelength region, indicating that the samples possess relatively high metallicity and plasmonic characteristics in the NIR. It is found that the carrier concentration dominates the electron effective mass and Drude plasma frequency. Although Au is a commonly used plasmonic material, at a wavelength of 1550 nm, the loss of SNO is 85.8% lower than that of Au, and its plasmonic performance metrics is significantly higher than TiN, Al:ZnO and Sn:In2O3, demonstrating the great potential of SNO in NIR plasmonic device applications.

Photon Momentum Enabled Light Absorption in Silicon

Photons do not carry sufficient momentum to induce indirect optical transitions in semiconducting materials, such as silicon, necessitating the assistance of lattice phonons to conserve momentum. Compared to direct bandgap semiconductors, this renders silicon a less attractive material for a wide variety of optoelectronic applications. In this work, we introduce an alternative strategy to fulfill the momentum-matching requirement in indirect optical transitions. We demonstrate that when confined to scales below ∼3 nm, photons acquire sufficient momentum to allow electronic transitions at the band edge of Si without the assistance of a phonon. Confined photons allow simultaneous energy and momentum conservation in two-body photon-electron scattering; in effect, converting silicon into a direct bandgap semiconductor. We show that this less-explored concept of light-matter interaction leads to a marked increase in the absorptivity of Si from the UV to the near-IR. The strategy provides opportunities for more efficient use of indirect semiconductors in photovoltaics, energy conversion, light detection, and emission.

High-Throughput On-Demand Design Platform for Plasmonic Nanocavities: A Wavefunction Theory Approach

Surface plasmon polaritons from plasmonic nanocavity have aroused great interest due to their applications in various fields, in which on-demand design is hindered by the lack of theoretical frameworks. Herein, based on its wave nature, we developed a wavefunction theory to explicitly describe individual surface plasmon polaritons and the resultant near-field and far-field behaviors, which serves as an efficient platform for high-throughput on-demand design of nanocavities. We found an applicative wavefunction form and proposed a two-body interaction function and a "shell" model for many-body interactions in surface plasmon polaritons' coupling. The wavefunction of individual surface plasmon polaritons and resultant near-field and far-field behaviors can be given explicitly and precisely. The theory provides a fundamental and quantitative understanding of surface plasmon polaritons and enables highly efficient on-demand design of plasmonic metamaterials and devices, leading to further methodological applications in numerous aspects.

Scalable and adaptable two-ligand co-solvent transfer methodology for gold bipyramids to organic solvents

Large and faceted nanoparticles, such as gold bipyramids, presently require synthesis using alkyl ammonium halide ligands in aqueous conditions to stabilize the structure, which impedes subsequent transfer and suspension of such nanoparticles in low polarity solvents despite success with few nanometer gold nanoparticles of shapes such as spheres. Phase transfer methodologies present a feasible avenue to maintain colloidal stability of suspensions and move high surface energy particles into organic solvent environments. Here, we present a method to yield stable suspensions of gold bipyramids in low-polarity solvents, including methanol, dimethylformamide, chloroform, and toluene, through the requisite combination of two capping agents and the presence of a co-solvent. By utilizing PEG-SH functionalization for stability, dodecanethiol (DDT) as the organic-soluble capping agent, and methanol to aid in the phase transfer, gold bipyramids with a wide-range of aspect ratios and sizes can be transferred between water and chloroform readily and maintain colloidal stability. Subsequent transfer to various organic and low-polarity solvents is then demonstrated for the first time.

Resonant Metasurfaces with Van Der Waals Hyperbolic Nanoantennas and Extreme Light Confinement

This work reports on a metasurface based on optical nanoantennas made of van der Waals material hexagonal boron nitride. The optical nanoantenna made of hyperbolic material was shown to support strong localized resonant modes stemming from the propagating high-k waves in the hyperbolic material. An analytical approach was used to determine the mode profile and type of cuboid nanoantenna resonances. An electric quadrupolar mode was demonstrated to be associated with a resonant magnetic response of the nanoantenna, which resembles the induction of resonant magnetic modes in high-refractive-index nanoantennas. The analytical model accurately predicts the modes of cuboid nanoantennas due to the strong boundary reflections of the high-k waves, a capability that does not extend to plasmonic or high-refractive-index nanoantennas, where the imperfect reflection and leakage of the mode from the cavity complicate the analysis. In the reported metasurface, excitations of the multipolar resonant modes are accompanied by directional scattering and a decrease in the metasurface reflectance to zero, which is manifested as the resonant Kerker effect. Van der Waals nanoantennas are envisioned to support localized resonances and can become an important functional element of metasurfaces and transdimensional photonic components. By designing efficient subwavelength scatterers with high-quality-factor resonances, this work demonstrates that this type of nanoantenna made of naturally occurring hyperbolic material is a viable substitute for plasmonic and all-dielectric nanoantennas in developing ultra-compact photonic components.

Photoelectrochemical Lithium Extraction from Waste Batteries

The amount of global hybrid-electric and all electric vehicle has increased dramatically in just five years and reached an all-time high of over 10 million units in 2022. A good deal of waste lithium (Li)-containing batteries from dead vehicles are invaluable unconventional resources with high usage of Li. However, the recycle of Li by green approaches is extremely inefficient and rare from waste batteries, giving rise to severe environmental pollutions and huge squandering of resources. Thus, in this mini review, we briefly summarized a green and promising route-photoelectrochemical (PEC) technology for extracting the Li from the waste lithium-containing batteries. This review first focuses on the critical factors of PEC performance, including light harvesting, charge-carrier dynamics, and surface chemical reactions. Subsequently, the conventional and PEC technologies applying in the area of Li recovery processes are analyzed and discussed in depth, and the potential challenges and future perspective for rational and healthy development of PEC Li extraction are provided positively.

Silver Nanoparticles: Synthesis, Structure, Properties and Applications

Silver nanoparticles (Ag NPs) have accumulated significant interest due to their exceptional physicochemical properties and remarkable applications in biomedicine, electronics, and catalysis sensing. This comprehensive review provides an in-depth study of synthetic approaches such as biological synthesis, chemical synthesis, and physical synthesis with a detailed overview of their sub-methodologies, highlighting advantages and disadvantages. Additionally, structural properties affected by synthesis methods are discussed in detail by examining the dimensions and surface morphology. The review explores the distinctive properties of Ag NPs, including optical, electrical, catalytic, and antimicrobial properties, which render them beneficial for a range of applications. Furthermore, this review describes the diverse applications in several fields, such as medicine, environmental science, electronics, and optoelectronics. However, with numerous applications, several kinds of issues still exist. Future attempts need to address difficulties regarding synthetic techniques, environmental friendliness, and affordability. In order to ensure the secure utilization of Ag NPs, it is necessary to establish sustainability in synthetic techniques and eco-friendly production methods. This review aims to give a comprehensive overview of the synthesis, structural analysis, properties, and multifaceted applications of Ag NPs.

Nanosized-laser-induced sub-20 nm homogenous alloy nanoparticles

Alloy nanoparticles (NPs) have great potential in nanosized 3D-printing, surface coating, plasmonic enhancement, information coding, and so forth. However, chemical-pollution-free and homogeneous sub-20 nm NPs maintain still a challenge in preparation. Here we present a smart nanosecond laser scan strategy of alloy-NPs preparation on a bilayer metal film by using a nanosized focused beam, successfully realizing controllable fabrication of the sub-20 nm homogeneous alloy NPs without pollution. As a demonstration, various sub-20 nm AgCu NPs with different volume ratios have been prepared, all NPs show narrow size distribution and uniform interparticle spacing. This simple and cost-effective method is stable and adaptable for other alloy-NPs such as AuAg NPs. In addition, such alloy NPs exhibit two-peak plasma resonance feature and information coding capacity. We believe that homogenous alloy sub-20 nm NPs will provide new application opportunities in many fields.

The Electromagnetic Noise Level Influence on the Laser Micro-Perforation Process Specific to Automotive Components

This article focuses on the influence of generated electromagnetic noise (energy) during the micro-perforation process. This study aims to investigate the critical parameters and effects of using laser technology in the processing of textile materials for airbags. Different levels of electromagnetic noise and material thicknesses were investigated to ensure the quality of manufactured parts and the best component performance. A factorial analysis (DOE) was developed to evaluate the influence of electromagnetic noise levels over pull test results and its effect on the micro-perforation process. The overall inferential analysis concludes a significant influence of the noise levels on micro-perforation processing. The detailed analysis suggests that 1.2 V is an optimal level of electromagnetic noise where the material maintains its mechanical properties in a more predictable and consistent manner. Additionally, the factorial design provides significant evidence for an interaction and main effects' influences of analyzed factors. The obtained results in this study have demonstrated that monitoring and controlling the noise level have beneficial effects over the laser processing. This ensures that the safety aspect of the produced parts is entirely upheld and protected. Also, this research contributes to improving the manufacturing process and ensures that high-quality products are obtained, being suitable for use in sensitive applications such as automotive airbags.

Surface Plasmon Resonance Modulation by Complexation of Platinum on the Surface of Silver Nanocubes

The use of plasmonic particles, specifically, localized surface plasmonic resonance (LSPR), may lead to a significant improvement in the electrical, electrochemical, and optical properties of materials. Chemical modification of the dielectric constant near the plasmonic surface should lead to a shift of the optical resonance and, therefore, the basis for color tuning and sensing. In this research, we investigated the variation of the LSPR by modifying the chemical environment of Ag nanoparticles (NPs) through the complexation of Pt(IV) metal cations near the plasmonic surface. This study is carried out by measuring the shift of the plasmon dipole resonance of Ag nanocubes (NCs) and nanowires (NWs) of differing sizes upon coating the Ag surface with a layer of polydopamine (PDA) as a coordinating matrix for Pt(IV) complexes. The red shift of up to 45 nm depends linearly on the thickness of the PDA/Pt(IV) layer and the Pt(IV) content. Additionally, we calculated the dielectric constant of the surrounding medium using a numerical method.