Plasmon-induced hot carriers in metallic nanoparticles

Plasmon-driven substitution of 4-mercaptophenylboronic acid to 4-nitrothiophenol monitored by surface-enhanced Raman spectroscopy

Plasmon-driven reactions on plasmonic nanoparticles (NPs) occur under significantly different conditions from those of classical organic synthesis and provide a promising pathway for enhancing the efficiency of various chemical processes. However, these reactions can also have undesirable effects, such as 4-mercaptophenylboronic acid (MPBA) deboronation. MPBA chemisorbs well to Ag NPs through its thiol group and can subsequently bind to diols, enabling the detection of various biological structures by surface-enhanced Raman scattering (SERS), but not upon its deboronation. To avoid this reaction, we investigated the experimental conditions of MPBA deboronation on Ag NPs by SERS. Our results showed that the level of deboronation strongly depends on both the morphology of the system and the excitation laser wavelength and power. In addition, we detected not only the expected products, namely thiophenol and biphenyl-4,4-dithiol, but also 4-nitrothiophenol (NTP). The crucial reagent for NTP formation was an oxidation product of hydroxylamine hydrochloride, the reduction agent used in Ag NP synthesis. Ultimately, this reaction was replicated by adding NaNO2 to the system, and its progress was monitored as a function of the laser power, thereby identifying a new reaction of plasmon-driven -B(OH)2 substitution for -NO2.

Plasmonic Bound States in the Continuum Metasurface-Semiconductor-Metal Architecture Enables Efficient Hot-Electron-Based Photodetector

Plasmonic hot-electron-based photodetectors (HEB-PDs) have received widespread attention for their ability to realize effective carrier collection under sub-bandgap illumination. However, due to the low hot electron emission probability, most of the existing HEB-PDs exhibit poor responsivity, which significantly restricts their practical applications. Here, by employing the binary-pore anodic alumina oxide template technique, we proposed a compact plasmonic bound state in continuum metasurface-semiconductor-metal-based (BIC M-S-M) HEB-PD. The symmetry-protected BIC can manipulate a strong gap surface plasmon in the stacked M-S-M structure, which effectively enhances light-matter interactions and improves the photoresponse of the integrated device. Notably, the optimal M-S-M HEB-PD with near-unit absorption (∼90%) around 800 nm delivers a responsivity of 5.18 A/W and an IPCE of 824.23% under 780 nm normal incidence (1 V external bias). Moreover, the ultrathin feature of BIC M-S-M (∼150 nm) on the flexible substrate demonstrates excellent stability under a wide range of illumination angles from -40° to 40° and at the curvature surface from 0.05 to 0.13 mm-1. The proposed plasmonic BIC strategy is very promising for many other hot-electron-related fields, such as photocatalysis, biosensing, imaging, and so on.

Boosting Electrochemiluminescence Performance of a Dual-Active Site Iron Single-Atom Catalyst-Based Luminol-Dissolved Oxygen System via Plasmon-Induced Hot Holes

Due to the commonly low content of biomarkers in diseases, increasing the sensitivity of electrochemiluminescence (ECL) systems is of great significance for in vitro ECL diagnosis and biodetection. Although dissolved O2 (DO) has recently been considered superior to H2O2 as a coreactant in the most widely used luminol ECL systems owing to its improved stability and less biotoxicity, it still has unsatisfactory ECL performance because of its ultralow reactivity. In this study, an effective plasmonic luminol-DO ECL system has been developed by complexing luminol-capped Ag nanoparticles (AgNPs) with plasma-treated Fe single-atom catalysts (Fe-SACs) embedded in graphitic carbon nitride (g-CN) (pFe-g-CN). Under optimal conditions, the performance of the resulting ECL system could be markedly increased up to 1300-fold compared to the traditional luminol-DO system. Further investigations revealed that duple binding sites of pFe-g-CN and plasmonically induced hot holes that disseminated from AgNPs to g-CN surfaces lead to facilitate significantly the luminous reaction process of the system. The proposed luminol-DO ECL system was further employed for the stable and ultrasensitive detection of prostate-specific antigen in a wide linear range of 1.0 fg/mL to 1 μg/mL, with a pretty low limit of detection of 0.183 fg/mL.

Plasmon-Induced Hot Electrons in Nanostructured Materials: Generation, Collection, and Application to Photochemistry

Plasmon refers to the coherent oscillation of all conduction-band electrons in a nanostructure made of a metal or a heavily doped semiconductor. Upon excitation, the plasmon can decay through different channels, including nonradiative Landau damping for the generation of plasmon-induced energetic carriers, the so-called hot electrons and holes. The energetic carriers can be collected by transferring to a functional material situated next to the plasmonic component in a hybrid configuration to facilitate a range of photochemical processes for energy or chemical conversion. This article centers on the recent advancement in generating and utilizing plasmon-induced hot electrons in a rich variety of hybrid nanostructures. After a brief introduction to the fundamentals of hot-electron generation and decay in plasmonic nanocrystals, we extensively discuss how to collect the hot electrons with various types of functional materials. With a focus on plasmonic nanocrystals made of metals, we also briefly examine those based upon heavily doped semiconductors. Finally, we illustrate how site-selected growth can be leveraged for the rational fabrication of different types of hybrid nanostructures, with an emphasis on the parameters that can be experimentally controlled to tailor the properties for various applications.

Raman Monitoring of the Electro-Optical Synergy-Induced Enhancements in Carbon-Bromine Bond Cleavage, Reaction Rate, and Product Selectivity of p-Bromothiophenol

Electro-optical synergy has recently been targeted to improve the separation of hot carriers and thereby further improve the efficiency of plasmon-mediated chemical reactions (PMCRs). However, the electro-optical synergy in PMCRs needs to be more deeply understood, and its contribution to bond dissociation and product selectivity needs to be clarified. Herein, the electro-optical synergy in plasmon-mediated reduction of p-bromothiophenol (PBTP) was studied on a plasmonic nanostructured silver electrode using in situ Raman spectroscopy and theoretical calculations. It was found that the electro-optical synergy-induced enhancements in the cleavage of carbon-bromine bonds, reaction rate, and product selectivity (4,4'-biphenyl dithiol vs thiophenol) were largely affected by the applied bias, laser wavelength, and laser power. The theoretical simulation further clarified that the strong electro-optical synergy is attributed to the matching of energy band diagrams of the plasmonic silver with those of the adsorbed PBTP molecules. A deep understanding of the electro-optical synergy in PBTP reduction and the clarification of the mechanism will be highly beneficial for the development of other highly efficient PMCRs.

Ab initio investigation of hot electron transfer in CO2 plasmonic photocatalysis in the presence of hydroxyl adsorbate

Photoreduction of carbon dioxide (CO2) on plasmonic structures is of great interest in photocatalysis to aid selectivity. While species commonly found in reaction environments and associated intermediates can steer the reaction down different pathways by altering the potential energy landscape of the system, they are often not addressed when designing efficient plasmonic catalysts. Here, we perform an atomistic study of the effect of the hydroxyl group (OH) on CO2 activation and hot electron generation and transfer using first-principles calculations. We show that the presence of OH is essential in breaking the linear symmetry of CO2, which leads to a charge redistribution and a decrease in the OCO angle to 134°, thereby activating CO2. Analysis of the partial density of states (pDOS) demonstrates that the OH group mediates the orbital hybridization between Au and CO2 resulting in more accessible states, thus facilitating charge transfer. By employing time-dependent density functional theory (TDDFT), we quantify the fraction of hot electrons directly generated into hybridized molecular states at resonance, demonstrating a broader energy distribution and an 11% increase in charge-transfer in the presence of OH groups. We further show that the spectral overlap between excitation energy and plasmon resonance plays a critical role in efficiently modulating electron transfer processes. These findings contribute to the mechanistic understanding of plasmon-mediated reactions and demonstrate the importance of co-adsorbed species in tailoring the electron transfer processes, opening new avenues for enhancing selectivity.

Hot carrier creation in a nanoparticle dimer-molecule composite

Light-matter interactions have garnered considerable interest owing to their burgeoning applications in quantum optics and plasmonics. Utilizing first principles calculations, this work explores the hot carrier (HC) generation and distribution within a composite system made up of a plasmonic nanoparticle dimer and linear polycyclic aromatic hydrocarbon (PAH) molecules. We examine the spatial and energetic distributions of HCs by initiating photoexcitation and allowing localized surface plasmon dephasing. By positioning PAH molecules within the plasmonic nanodimer's gap region, our investigation uncovers HC tuning. Notably, depending on the size of the PAH molecules, there are significant alterations in the HC distribution. Hot electrons (HEs) are distributed across both the nanodimer and the PAH molecule, while hot holes (HHs) become entirely localized on the PAH as the PAH grows larger. These findings improve our understanding of plasmon-molecule coupled states and provide guidance on how to customize HC distributions through the creation of hybrid plasmonic materials.

New Nanophotonics Approaches for Enhancing the Efficiency and Stability of Perovskite Solar Cells

Over the past decade, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has experienced a remarkable ascent, soaring from 3.8% in 2009 to a remarkable record of 26.1% in 2023. Many recent approaches for improving PSC performance employ nanophotonic technologies, from light harvesting and thermal management to the manipulation of charge carrier dynamics. Plasmonic nanoparticles and arrayed dielectric nanostructures have been applied to tailor the light absorption, scattering, and conversion, as well as the heat dissipation within PSCs to improve their PCE and operational stability. In this review, it is begin with a concise introduction to define the realm of nanophotonics by focusing on the nanoscale interactions between light and surface plasmons or dielectric photonic structures. Prevailing strategies that utilize resonance-enhanced light-matter interactions for boosting the PCE and stability of PSCs from light trapping, carrier transportation, and thermal management perspectives are then elaborated, and the resultant practical applications, such as semitransparent photovoltaics, colored PSCs, and smart perovskite windows are discussed. Finally, the state-of-the-art nanophotonic paradigms in PSCs are reviewed, and the benefits of these approaches in improving the aesthetic effects and energy-saving character of PSC-integrated buildings are highlighted.

Phototransformation of achiral metasurfaces into handedness-selectable transient chiral media

Chirality is a geometric property describing the lack of mirror symmetry. This unique feature enables photonic spin-selectivity in light-matter interaction, which is of great significance in stereochemistry, drug development, quantum optics, and optical polarization control. The versatile control of optical geometry renders optical metamaterials as an effective platform for engineered chiral properties at prescribed spectral regimes. Unfortunately, geometry-imposed restrictions only allow one circular polarization state of photons to effectively interact with chiral meta-structures. This limitation motivates the idea of discovering alternative techniques for dynamically reconfiguring the chiroptical responses of metamaterials in a fast and facile manner. Here, we demonstrate an approach that enables optical, sub-picosecond conversion of achiral meta-structures to transient chiral media in the visible regime with desired handedness upon the inhomogeneous generation of plasmonic hot electrons. As a proof of concept, we utilize linearly polarized laser pulse to demonstrate near-complete conversion of spin sensitivity in an achiral meta-platform-a functionality yet achieved in a non-mechanical fashion. Owing to the generation, diffusion, and relaxation dynamics of hot electrons, the demonstrated technique for all-optical creation of chirality is inherently fast, opening new avenues for ultrafast spectro-temporal construction of chiral platforms with on-demand spin-selectivity.

Plasmon-induced hot carrier distribution in a composite nanosystem: role of the adsorption site

The generation of hot carriers (HCs) through the excitation of localized surface plasmon resonance (LSPR) in metal nanostructures is a fascinating phenomenon that fuels both fundamental and applied research. However, gaining insights into HCs at a microscopic level has posed a complex challenge, limiting our ability to create efficient nanoantennas that utilize these energized carriers. In this investigation, we employ real-time time-dependent density functional theory (rt-TDDFT) calculations to examine the creation and distribution of HCs within a model composite system consisting of a silver (Ag) nanodisk and a carbon monoxide (CO) molecule. We find that the creation and distribution of HCs are notably affected by the CO adsorption site. Particularly, when the CO molecule adsorbs onto the hollow site of the Ag nanodisk, it exhibits the highest potential among various composite systems in terms of structural stability, enhanced orbital hybridization, and HC generation and transfer. Utilizing a Gaussian laser pulse adjusted to match the LSPR frequency, we observe a marked buildup of hot electrons and hot holes on the C and O atoms. Conversely, the region encompassing the C-O bond exhibits a depletion of hot electrons and hot holes. We believe that these findings could have significant implications in the field of HC photocatalysis.

Plasmon induced hot carrier distribution in Ag20 -CO composite

The interaction between plasmons and the molecules leads to the transfer of plasmon-induced hot carriers, presenting innovative opportunities for controlling chemical reactions on sub-femtosecond timescales. Through real-time time-dependent density functional theory simulations, we have investigated the enhancement of the electric field due to plasmon excitation and the subsequent generation and transfer of plasmon-induced hot carriers in a linear atomic chain of Ag20 and an Ag20 -CO composite system. By applying a Gaussian laser pulse tuned to align with the plasmon frequency, we observe a plasmon-induced transfer of hot electrons from the occupied states of Ag to the unoccupied molecular orbitals of CO. Remarkably, there is a pronounced accumulation of hot electrons and hot holes on the C and O atoms. This phenomenon arises from the electron migration from the inter-nuclear regions of the C-O bond towards the individual C and O atoms. The insights garnered from our study hold the potential to drive advancements in the development of more efficient systems for catalytic processes empowered by plasmonic interactions.

Tailoring Hot-Carrier Distributions of Plasmonic Nanostructures through Surface Alloying

Alloyed metal nanoparticles are a promising platform for plasmonically enabled hot-carrier generation, which can be used to drive photochemical reactions. Although the non-plasmonic component in these systems has been investigated for its potential to enhance catalytic activity, its capacity to affect the photochemical process favorably has been underexplored by comparison. Here, we study the impact of surface alloy species and concentration on hot-carrier generation in Ag nanoparticles. By first-principles simulations, we photoexcite the localized surface plasmon, allow it to dephase, and calculate spatially and energetically resolved hot-carrier distributions. We show that the presence of non-noble species in the topmost surface layer drastically enhances hot-hole generation at the surface at the expense of hot-hole generation in the bulk, due to the additional d-type states that are introduced to the surface. The energy of the generated holes can be tuned by choice of the alloyant, with systematic trends across the d-band block. Already low surface alloy concentrations have a large impact, with a saturation of the enhancement effect typically close to 75% of a monolayer. Hot-electron generation at the surface is hindered slightly by alloying, but here a judicious choice of the alloy composition allows one to strike a balance between hot electrons and holes. Our work underscores the promise of utilizing multicomponent nanoparticles to achieve enhanced control over plasmonic catalysis and provides guidelines for how hot-carrier distributions can be tailored by designing the electronic structure of the surface through alloying.

Ultrafast hot-carrier dynamics in ultrathin monocrystalline gold

Applications in photodetection, photochemistry, and active metamaterials and metasurfaces require fundamental understanding of ultrafast nonthermal and thermal electron processes in metallic nanosystems. Significant progress has been recently achieved in synthesis and investigation of low-loss monocrystalline gold, opening up opportunities for its use in ultrathin nanophotonic architectures. Here, we reveal fundamental differences in hot-electron thermalisation dynamics between monocrystalline and polycrystalline ultrathin (down to 10 nm thickness) gold films. Comparison of weak and strong excitation regimes showcases a counterintuitive unique interplay between thermalised and non-thermalised electron dynamics in mesoscopic gold with the important influence of the X-point interband transitions on the intraband electron relaxation. We also experimentally demonstrate the effect of hot-electron transfer into a substrate and the substrate thermal properties on electron-electron and electron-phonon scattering in ultrathin films. The hot-electron injection efficiency from monocrystalline gold into TiO2, approaching 9% is measured, close to the theoretical limit. These experimental and modelling results reveal the important role of crystallinity and interfaces on the microscopic electronic processes important in numerous applications.

Peeking into the Femtosecond Hot-Carrier Dynamics Reveals Unexpected Mechanisms in Plasmonic Photocatalysis

Plasmonic-driven photocatalysis may lead to reaction selectivity that cannot be otherwise achieved. A fundamental role is played by hot carriers, i.e., electrons and holes generated upon plasmonic decay within the metal nanostructure interacting with molecular species. Understanding the elusive microscopic mechanism behind such selectivity is a key step in the rational design of hot-carrier reactions. To accomplish that, we present state-of-the-art multiscale simulations, going beyond density functional theory, of hot-carrier injections for the rate-determining step of a photocatalytic reaction. We focus on carbon dioxide reduction, for which it was experimentally shown that the presence of a rhodium nanocube under illumination leads to the selective production of methane against carbon monoxide. We show that selectivity is due to a (predominantly) direct hole injection from rhodium to the reaction intermediate CHO. Unexpectedly, such an injection does not promote the selective reaction path by favoring proper bond breaking but rather by promoting bonding of the proper molecular fragment to the surface.

Effect of hot electron induced charge transfer generated by surface plasmon resonance on Ag@Au/ITO/PNTP systems

The present study discusses the fabrication of a bimetallic material consisting of silver nanorods and gold nanospheres (designated Ag@Au), and its surface modification with 4-nitrothiophenol (PNTP) after deposition on an indium tin oxide (ITO) glass sheet, followed by laser irradiation at various wavelengths. The results indicate that the reduction of PNTP is more complete under irradiation at 532 nm due to the surface plasmon resonance (SPR) effects of the gold and silver nanomaterials. Moreover, the surface enhanced Raman scattering (SERS) of the PNTP adsorbed on the Ag@Au/ITO is found to be significantly stronger than that of PNTP adsorbed on Ag@Au alone, due to charge transfer (CT) at the interface. In addition, the SERS enhancement effect of the PNTP molecules on the Ag@Au/ITO substrate is optimal under 532 nm laser irradiation due to the hot electron-induced CT generated by the SPR effect. Thus, the system constructed herein combines the effects of SPR and CT, thereby assisting in a further understanding of the enhancement mechanism of SERS and, hence, the further development SERS research in metal-semiconductor-molecular systems.

Tailoring linear and nonlinear plasmons of metal/MoS2/metal nanostructures

We investigated the linear and nonlinear response of the localized surface plasmons (LSPs) and surface plasmon polaritons (SPPs) in metal and MoS2 nanostructures. The results show that the response of LSPs and SPPs has an important influence on the energy exchange. SPPs with unique non-radiative characteristics can be used as energy recovery tanks to reuse the radiated energy of LSPs and promote the production of hot carriers. The energy exchange through plasmon modes can promote the transfer of hot electrons in the Au grating, the MoS2 layer, and the metal film. The fundamental field induces the increase of the second harmonic wave by introducing the second-order nonlinear source. In addition, the evolution of the lifetime of linear and nonlinear plasmonic modes is also investigated to study the underlying mechanism of the micro process in the plasmonic-photonic interaction. The plasmonic energy exchanging configuration overcomes the challenge by utilizing hot carriers. It is instructive in terms of improving the linear and nonlinear performance of plasmonic opto-electronic devices.

Molecular Orbital Insights into Plasmon-Induced Methane Photolysis

As a promising way to reduce the temperature for conventional thermolysis, plasmon-induced photocatalysis has been utilized for the dehydrogenation of methane. Here we probe the microscopic dynamic mechanism for plasmon-induced methane dissociation over a tetrahedral Ag20 nanoparticle with molecular orbital insights using time-dependent density functional theory. We ingeniously built the relationship between the chemical bonds and molecular orbitals via Hellmann-Feynman forces. The time- and energy-resolved photocarrier analysis shows that the indirect hot hole transfer from the Ag nanoparticle to methane dominates the photoreaction at low laser intensity, due to the strong hybridization of the Ag nanoparticle and CH4 orbitals, while indirect and direct charge transfer coexist to facilitate methane dissociation in intense laser fields. Our findings can be used to design novel methane photocatalysts and highlight the broad prospects of the molecular orbital approach for adsorbate-substrate systems.

Boosting the Plasmon-Mediated Electrochemical Oxidation of p-Aminothiophenol with p-Hydroxythiophenol as Molecular Cocatalyst

Plasmon-mediated electrochemistry is an emerging area of interest in which the electrochemical reactions are enhanced by employing metal nanostructures possessing localized surface plasmon resonance (LSPR). However, the reaction efficacy is still far below its theoretical limit due to the ultrafast relaxation of LSPR-generated hot carriers. Herein, we introduce p-hydroxythiophenol (PHTP) as a molecular cocatalyst to significantly improve the reaction efficacy in plasmon-mediated electrochemical oxidation of p-aminothiophenol (PATP) on gold nanoparticles. Using electrochemical techniques, in situ Raman spectroscopy, and theoretical calculations, we elucidate that the presence of PHTP improves the hot hole-mediated electrochemical oxidation of PATP by 2-fold through the trapping of plasmon-mediated hot electrons. In addition, the selectivity of PATP oxidation could also be modulated by the introduction of PHTP cocatalyst. This tactic of employing molecular cocatalyst can be drawn out to endorse various plasmonic electrochemical reactions because of its simple protocol, high efficiency, and high selectivity.

All-in-one self-floating porous foams as robust heat-blocking layers for efficient photothermal conversion and solar desalination

Solar-driven interfacial evaporation is a highly efficient and ecofriendly technology for producing freshwater. Herein, self-floating plasmon Ag/black TiO2/carbon porous layered foams (Ag-BTCFs) were demonstrated as efficient solar-thermal convectors using freeze-drying cast-molding and high-temperature surface hydrogenation strategies. This all-in-one three-dimensional (3D) cross-linked self-floating porous layered foam material with full-spectrum absorption can fully harvest sunlight (∼95.45%) and effectively block heat transfer to its sublayer. The synergy of sufficient utilization of absorbed ultraviolet radiation by black TiO2 (b-TiO2), visible light absorption by Ag nanoparticles (Ag NPs) via localized surface plasmon resonance, and near-infrared absorption by layered-amorphous carbon can achieve full-solar-spectrum absorption to concentrate thermal energy. In addition to their synergistic effect, they are conducive to the relaxation of hot electrons when utilizing photogenerated holes to degrade pollutants in domestic wastewater. The steam generation efficiency of Ag-BTCFs is up to 1.79 kg m-2h-1 due to their solar energy conversion efficiency of 81.74% under 1 sun irradiation, which is five times higher than the evaporation rate of pure water. Notably, the material's efficient ion removal rate of 99.80% for solar desalination indicates its high potential for various applications. This strategy provides new insights for fabricating recyclable heat-blocking layer systems against thermal loss to enhance solar steam generation.

Theory and modeling of light-matter interactions in chemistry: current and future

Light-matter interaction not only plays an instrumental role in characterizing materials' properties via various spectroscopic techniques but also provides a general strategy to manipulate material properties via the design of novel nanostructures. This perspective summarizes recent theoretical advances in modeling light-matter interactions in chemistry, mainly focusing on plasmon and polariton chemistry. The former utilizes the highly localized photon, plasmonic hot electrons, and local heat to drive chemical reactions. In contrast, polariton chemistry modifies the potential energy curvatures of bare electronic systems, and hence their chemistry, via forming light-matter hybrid states, so-called polaritons. The perspective starts with the basic background of light-matter interactions, molecular quantum electrodynamics theory, and the challenges of modeling light-matter interactions in chemistry. Then, the recent advances in modeling plasmon and polariton chemistry are described, and future directions toward multiscale simulations of light-matter interaction-mediated chemistry are discussed.

Evidence of Surface-Mediated Carrier-Phonon Scattering in MXene

In a two-dimensional (2D) metallic nanostructure, when a sample's thickness is shorter than a carrier mean free path, the ultrathin thickness may influence carrier and energy transport, owing to surface scattering. However, to date, for metallic 2D transition-metal carbides (MXenes), experiments and calculations related to surface scattering have not been performed. The contribution of ultrathin structures to carrier surface scattering in MXene is yet to be explored. Herein, to reveal this effect, we design various models, including metal/MXene, dielectric/MXene, and bulk structure, and analyze their carrier dynamics via ultrafast spectroscopy. The results related to carrier dynamics indicate that the influence of the dielectric/MXene interface and the temperature is negligible. In contrast, the carrier dynamic lifetimes are prolonged owing to weakened surface scattering in metal/MXene, which is supported by ab initio calculations. These results suggest that the carrier-phonon scattering is dominated by surface scattering. These findings can help guide effective energy transport and enhance energy conversion and catalysis.

Reconstruction of the Near-Field Electric Field by SNOM Measurement

Scanning near-field optical microscope (SNOM) with nanoscale spatial resolution has been a powerful tool in studying the plasmonic properties of nano materials/structures. However, the quantification of the SNOM measurement remains a major challenge in the field due to the lack of reliable methodologies. We employed the point-dipole model to describe the tip-surface interaction upon laser illumination and theoretically derived the quantitative relationship between the measured results and the actual near-field electric field strength. Thus, we can experimentally reconstruct the near-field electric field through this theoretically calculated relationship. We also developed an experimental technique together with FEM simulation to get the above relationship experimentally and reconstruct the near-field electric field from the measurement by SNOM.

Plasmon induced hot carrier generation in a pyridine@Au20 composite

Using time-dependent density functional theory calculations, we have investigated the generation of hot carriers (HCs) in a system comprising a pyridine molecule and a tetrahedral Au20 plasmonic cluster. Our findings indicate that the decay of the localized surface plasmon resonance (LSPR) induced in the pyridine@Au20 system by a laser pulse facilitates the direct transfer of hot electrons from the occupied states of the Au20 cluster to the unoccupied molecular orbitals of pyridine. Notably, we have identified that the interparticle gap distance between the Au20 cluster and the pyridine molecule plays a critical role in controlling the generation of HCs. By precisely controlling the interaction between the plasmonic cluster and the molecule, we can effectively manipulate the energy distribution of the generated HCs. These insights have the potential to drive advancements in the development of more efficient systems for plasmonic catalysis.

Quantifying the ultrafast and steady-state molecular reduction potential of a plasmonic photocatalyst

Plasmonic materials are promising photocatalysts as they are well suited to convert light into hot carriers and heat. Hot electron transfer is suggested as the driving force in many plasmon-driven reactions. However, to date, there are no direct molecular measures of the rate and yield of plasmon-to-molecule electron transfer or energy of these electrons on the timescale of plasmon decay. Here, we use ultrafast and spectroelectrochemical surface-enhanced Raman spectroscopy to quantify electron transfer from a plasmonic substrate to adsorbed methyl viologen molecules. We observe a reduction yield of 2.4 to 3.5% on the picosecond timescale, with plasmon-induced potentials ranging from [Formula: see text]3.1 to [Formula: see text]4.5 mV. Excitingly, some of these reduced species are stabilized and persist for tens of minutes. This work provides concrete metrics toward optimizing material-molecule interactions for efficient plasmon-driven photocatalysis.

Ligand-mediated electron transport channels enhance photocatalytic activity of plasmonic nanoparticles

Photoexcitation of noble metal nanoparticles creates surface plasmons which further decay to form energetic charge carriers. These charge carriers can initiate and/or accelerate various chemical processes at nanoparticle surfaces, although the efficiency of such processes remains low as a large fraction of these carriers recombine before they can reach the reaction sites. Thus efficient utilization of these charge carriers requires designing nanostructures that promote the separation of charges and their transport toward the reaction sites. Here we demonstrate that covalently bound surface-coating ligands with suitable orbital alignment can provide electron transport channels boosting hot electron extraction from a gold nanostructure leading to a huge enhancement in the rate of hydrogen evolution reaction (HER) under NIR excitation. A (p)Br-Ph-SH substituted gold nanoprism (AuTP) substrate produced ∼4500 fold more hydrogen compared to a pristine AuTP substrate under 808 nm excitation. Further experimental and theoretical studies on a series of substituted benzene-thiol bound AuTP substrates showed that the extent of the ligand-mediated HER enhancement depends not only on the polarity of the ligand but on the interfacial orbitals interactions.

Tracking light-induced charge transport

Precise charge dynamics could help to improve the operation of solar cells and sensors.

Theory of Hot-Carrier Generation in Bimetallic Plasmonic Catalysts

Bimetallic nanoreactors in which a plasmonic metal is used to funnel solar energy toward a catalytic metal have recently been studied experimentally, but a detailed theoretical understanding of these systems is lacking. Here, we present theoretical results of hot-carrier generation rates of different Au-Pd nanoarchitectures. In particular, we study spherical core-shell nanoparticles with a Au core and a Pd shell as well as antenna-reactor systems consisting of a large Au nanoparticle that acts as an antenna and a smaller Pd satellite nanoparticle separated by a gap. In addition, we investigate an antenna-reactor system in which the satellite is a core-shell nanoparticle. Hot-carrier generation rates are obtained from an atomistic quantum-mechanical modeling technique which combines a solution of Maxwell's equation with a tight-binding description of the nanoparticle electronic structure. We find that antenna-reactor systems exhibit significantly higher hot-carrier generation rates in the catalytic material than the core-shell system as a result of strong electric field enhancements associated with the gap between the antenna and the satellite. For these systems, we also study the dependence of the hot-carrier generation rate on the size of the gap, the radius of the antenna nanoparticle, and the direction of light polarization. Overall, we find a strong correlation between the calculated hot-carrier generation rates and the experimentally measured chemical activity for the different Au-Pd photocatalysts. Our insights pave the way toward a microscopic understanding of hot-carrier generation in heterogeneous nanostructures for photocatalysis and other energy-conversion applications.

Plasmon-Determined Selectivity in Photocatalytic Transformations on Gold and Gold-Palladium Nanostructures

Noble metal nanostructures absorb light producing coherent oscillations of the metal's electrons, so-called localized surface plasmon resonances (LSPRs). LSPRs can decay generating hot carriers, highly energetic species that trigger chemical transformations in the molecules located on the metal surfaces. The number of chemical reactions can be expanded by coupling noble and catalytically active metals. However, it remains unclear whether such mono- and bimetallic nanostructures possess any sensitivity toward one or another chemical reaction if both of them can take place in one molecular analyte. In this study, we utilize tip-enhanced Raman spectroscopy (TERS), an emerging analytical technique that has single-molecule sensitivity and sub-nanometer spatial resolution, to investigate plasmon-driven reactivity of 2-nitro-5-thiolobenzoic acid (2-N-5TBA) on gold and gold@palladium nanoplates (AuNPs and Au@PdNPs). This molecular analyte possesses both nitro and carboxyl groups, which can be reduced or removed by hot carriers. We found that on AuNPs, 2-N-5TBA dimerized forming 4,4'-dimethylazobenzene (DMAB), the bicarbonyl derivative of DMAB, as well as 4-nitrobenzenethiol (4-NBT). Our accompanying theoretical investigation based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) confirmed these findings. The theoretical analysis shows that 2-N-5TBA first dimerized forming the bicarbonyl derivative of DMAB, which then decarboxylated forming DMAB. Finally, DMAB can be further reduced leading to 4-NBT. This reaction mechanism is supported by TERS-determined yields on these three molecules on AuNPs. We also found that on Au@PdNPs, 2-N-5TBA first formed the bicarbonyl derivative of DMAB, which is then reduced to both bihydroxyl-DMAB and 4-amino-3-mercaptobenzoic acid. The yield of these reaction products on Au@PdNPs strictly follows the free-energy potential of these molecules on the metallic surfaces.

Promoting plasmonic photocatalysis with ligand-induced charge separation under interband excitation

Plasmonic nanoparticles have been demonstrated to enhance photocatalysis due to their strong photon absorption and efficient hot-carrier generation. However, plasmonic photocatalysts suffer from a short lifetime of plasmon-generated hot carriers that decay through internal relaxation pathways before being harnessed for chemical reactions. Here, we demonstrate the enhanced photocatalytic reduction of gold ions on gold nanorods functionalized with polyvinylpyrrolidone. The catalytic activities of the reaction are quantified by in situ monitoring of the spectral evolution of single nanorods using a dark-field scattering microscope. We observe a 13-fold increase in the reduction rate with the excitation of d-sp interband transition compared to dark conditions, and a negligible increase in the reduction rate when excited with intraband transition. The hole scavenger only plays a minor role in the photocatalytic reduction reaction. We attribute the enhanced photocatalysis to an efficient charge separation at the gold-polyvinylpyrrolidone interface, where photogenerated d-band holes at gold transfer to the HOMO of polyvinylpyrrolidone, leading to the prolonged lifetime of the electrons that subsequently reduce gold ions to gold atoms. These results provide new insight into the design of plasmonic photocatalysts with capping ligands.

Promises of Plasmonic Antenna-Reactor Systems in Gas-Phase CO2 Photocatalysis

Sunlight-driven photocatalytic CO2 reduction provides intriguing opportunities for addressing the energy and environmental crises faced by humans. The rational combination of plasmonic antennas and active transition metal-based catalysts, known as "antenna-reactor" (AR) nanostructures, allows the simultaneous optimization of optical and catalytic performances of photocatalysts, and thus holds great promise for CO2 photocatalysis. Such design combines the favorable absorption, radiative, and photochemical properties of the plasmonic components with the great catalytic potentials and conductivities of the reactor components. In this review, recent developments of photocatalysts based on plasmonic AR systems for various gas-phase CO2 reduction reactions with emphasis on the electronic structure of plasmonic and catalytic metals, plasmon-driven catalytic pathways, and the role of AR complex in photocatalytic processes are summarized. Perspectives in terms of challenges and future research in this area are also highlighted.

In Situ Electron Microscopy of Transformations of Copper Nanoparticles under Plasmonic Excitation

Metal nanoparticles are attracting interest for their light-absorption properties, but such materials are known to dynamically evolve under the action of chemical and physical perturbations, resulting in changes in their structure and composition. Using a transmission electron microscope equipped for optical excitation of the specimen, the structural evolution of Cu-based nanoparticles under simultaneous electron beam irradiation and plasmonic excitation was investigated with high spatiotemporal resolution. These nanoparticles initially have a Cu core-Cu₂O oxide shell structure, but over the course of imaging, they undergo hollowing via the nanoscale Kirkendall effect. We captured the nucleation of a void within the core, which then rapidly grows along specific crystallographic directions until the core is hollowed out. Hollowing is triggered by electron-beam irradiation; plasmonic excitation enhances the kinetics of the transformation likely by the effect of photothermal heating.

Vibrationally Hot Reactants in a Plasmon-Assisted Chemical Reaction

Recent studies on plasmon-assisted chemical reactions postulate that the hot electrons of plasmon-excited nanostructures may induce a non-thermal vibrational activation of metal-bound reactants. However, the postulate has not been fully validated at the level of molecular quantum states. We directly and quantitatively prove that such activation occurs on plasmon-excited nanostructures: The anti-Stokes Raman spectra of reactants undergoing a plasmon-assisted reaction reveal that a particular vibrational mode of the reactant is selectively excited, such that the reactants possess >10 times more energy in the mode than is expected from the fully thermalized molecules at the given local temperature. Furthermore, a significant portion (∼20%) of the excited reactant is in vibrational overtone states with energies exceeding 0.5 eV. Such mode-selective multi-quantum excitation could be fully modeled by the resonant electron-molecule scattering theory. Such observations suggest that the vibrationally hot reactants are created by non-thermal hot electrons, not by thermally heated electrons or phonons of metals. The result validates the mechanism of plasmon-assisted chemical reactions and further offers a new method to explore the vibrational reaction control on metal surfaces.

Insights into Plasmon-Induced Dimerization of Rhodanine-A Surface-Enhanced Raman Scattering Study

Plasmon-mediated chemical reactions (PMCRs) have attracted considerable interest in recent times. The PMCR initiated by hot carriers is known to be influenced by the type of metals and the excitation wavelength. Herein, we have carried out the surface-enhanced Raman scattering (SERS) investigation of rhodanine (Rd), an important pharmacologically active heterocyclic compound, adsorbed on silver and gold nanoparticles (AgNP and AuNP) using 514.5 and 632.8 nm lasers. The prominent Raman band at 1566 cm^-1 observed in the SERS spectra is attributed to the characteristic ν(C═C) stretching vibration of the Rd dimer and not of Rd tautomers. The chemical transformation of Rd to Rd dimer on metal surfaces is plausibly triggered by the indirect transfer of energetic hot electrons generated during the non-radiative decay of plasmon. The mechanism involved in the dimerization of Rd via the indirect transfer of hot electrons is also presented. The effect of wavelength on the dimerization of Rd is also observed on the AgNP surface, which indicates that the dimerization occurs more efficiently on the AgNP surface with excitation at 514.5 nm wavelength.

Molecular dynamics study of plasmon-mediated chemical transformations

Heterogeneous catalysis of adsorbates on metallic surfaces mediated by plasmons has potential high photoelectric conversion efficiency and controllable reaction selectivity. Theoretical modeling of dynamical reaction processes enables in-depth analyses complementing experimental investigations. Especially for plasmon-mediated chemical transformations, light absorption, photoelectric conversion, electron-electron scattering, and electron-phonon coupling occur simultaneously on different timescales, making it very challenging to delineate the complex interplay of different factors. In this work, a trajectory surface hopping non-adiabatic molecular dynamics method is used to investigate the dynamics of plasmon excitation in an Au₂₀-CO system, including hot carrier generation, plasmon energy relaxation, and CO activation induced by electron-vibration coupling. The electronic properties indicate that when Au₂₀-CO is excited, a partial charge transfer takes place from Au₂₀ to CO. On the other hand, dynamical simulations show that hot carriers generated after plasmon excitation transfer back and forth between Au₂₀ and CO. Meanwhile, the C-O stretching mode is activated due to non-adiabatic couplings. The efficiency of plasmon-mediated transformations (∼40%) is obtained based on the ensemble average of these quantities. Our simulations provide important dynamical and atomistic insights into plasmon-mediated chemical transformations from the perspective of non-adiabatic simulations.

Photothermal Nanomaterials: A Powerful Light-to-Heat Converter

All forms of energy follow the law of conservation of energy, by which they can be neither created nor destroyed. Light-to-heat conversion as a traditional yet constantly evolving means of converting light into thermal energy has been of enduring appeal to researchers and the public. With the continuous development of advanced nanotechnologies, a variety of photothermal nanomaterials have been endowed with excellent light harvesting and photothermal conversion capabilities for exploring fascinating and prospective applications. Herein we review the latest progresses on photothermal nanomaterials, with a focus on their underlying mechanisms as powerful light-to-heat converters. We present an extensive catalogue of nanostructured photothermal materials, including metallic/semiconductor structures, carbon materials, organic polymers, and two-dimensional materials. The proper material selection and rational structural design for improving the photothermal performance are then discussed. We also provide a representative overview of the latest techniques for probing photothermally generated heat at the nanoscale. We finally review the recent significant developments of photothermal applications and give a brief outlook on the current challenges and future directions of photothermal nanomaterials.

Ultrabroadband hot-hole photodetector based on ultrathin gold film

Hot carriers injected into semiconductor enables below-bandgap photodetection, thus attracting increasing interest. The performance of hot carrier-based device is directly related to the absorptivity of metal. Several strategies such as surface plasmons, metamaterials, and optical cavities are utilized to enhance the weak intrinsic absorption of the metal. However, the detection range is limited by their narrow resonance bandwidth alternatively. Impedance-matched absorbers, whose sheet resistance is equal to half of the free-space impedance (188 Ω), can achieve a wavelength-independent absorptivity up to 50%. Herein, we theoretically design a purely planar hot-hole photodetector based on ultrathin gold film, a new type of metallic impedance-matched absorber. Benefiting both from the efficient absorption and ultrathin nature of the film, we predict that the photoresponsivity of our device can reach 35.7 mA W^-1 under zero bias at the wavelength of 1.3 μm, with a full width at half maximum (FWHM) of detection range reaching 1050 nm, setting a new record for the bandwidth of the hot carrier photodetectors. We also demonstrated that the device is robust to the incident angle and can be tuned through the external bias voltage. This work provides a pathway for broadband hot carrier detectors and other hot carrier-based applications.

Enhanced plasmonic photocatalytic performance of C3N4/Cu by the introduction of a reduced graphene oxide interlayer

Cu nanoparticles (NPs) are low-cost surface plasmonic resonance (SPR) metal nanostructures, and their SPR properties can be used to enhance the photocatalytic hydrogen evolution performance of carbon nitride (C₃N₄). But their actual performance is usually limited, and one key factor is their poor interfacial quality. In this work, a highly conductive reduced graphene oxide (RGO) interlayer is introduced between protonated C₃N₄ (PCN) nanosheets and Cu NPs, which can act as an efficient sink for photogenerated electrons from C₃N₄ and hot electrons from Cu NPs, and simultaneously serve as reaction sites for the hydrogen evolution reaction, and accelerate the charge transport by the formed C-O-C and C-O-Cu bonds. The optimal hydrogen evolution rate of the optimized PCN/RGO/Cu is 1.30 mmol g^-1 h^-1, which is 6.76, 2.47 and 2.41 times that of PCN, PCN/RGO and PCN/Cu, respectively, and it can further reach up to 13.22 mmol g^-1 h^-1 by loading moderate Pt NPs. Meanwhile, the introduced RGO can effectively anchor Cu NPs to enhance the stability of the photocatalyst. In addition, due to the broad SPR response of Cu NPs, a near-infrared photocatalytic performance is realized for PCN/RGO/Cu with an apparent quantum efficiency of 0.46% at 765 nm.

Recent progress of cocatalysts loaded on carbon nitride for selective photoreduction of CO2 to CH4

A photocatalytic system driven by solar light is one of the promising strategies for converting CO₂ into valuable energy. The reduction of CO₂ to CH₄ is widely studied since CH₄ has a high energy density as the main component of nonrenewable natural gas. Therefore, it is necessary to develop semiconductor materials with high photocatalytic activity and CH₄ selectivity. Graphitic carbon nitride (g-C₃N₄/CN) has attracted widespread attention for photocatalytic CO₂ reduction due to its excellent redox ability and visible light response. A hybrid system constructed by loading cocatalysts on g-C₃N₄ can significantly improve the yield of target products, and serve as a general platform to explore the mechanism of the CO₂ reduction reaction. Herein, we briefly introduce the theory of selective CO₂ photoreduction and the basic properties of cocatalysts. Then, several typical configurations and modification strategies of cocatalyst/CN systems for promoting CH₄ selective production are presented in detail. In particular, we systematically summarize the application of cocatalyst/CN composite photocatalysts in the selective reduction of CO₂ to methane, according to the classification of cocatalysts (monometal, bimetal, metal-based compound, and nanocarbon materials). Finally, the challenges and perspectives for developing cocatalyst/g-C₃N₄ systems with high CH₄ selectivity are presented to guide the rational design of catalysts with high performance in the future.

Energy Transfer to Molecular Adsorbates by Transient Hot Electron Spillover

Hot electron (HE) photocatalysis is one of the most intriguing fields of nanoscience, with a clear potential for technological impact. Despite much effort, the mechanisms of HE photocatalysis are not fully understood. Here we investigate a mechanism based on transient electron spillover on a molecule and subsequent energy release into vibrational modes. We use state-of-the-art real-time Time Dependent Density Functional Theory (rt-TDDFT), simulating the dynamics of a HE moving within linear chains of Ag or Au atoms, on which CO, N₂, or H₂O are adsorbed. We estimate the energy a HE can release into adsorbate vibrational modes and show that certain modes are selectively activated. The energy transfer strongly depends on the adsorbate, the metal, and the HE energy. Considering a cumulative effect from multiple HEs, we estimate this mechanism can transfer tenths of an eV to molecular vibrations and could play an important role in HE photocatalysis.

Narrowband HgCdTe infrared photodetector with integrated plasmonic structure

The application of plasmonic structure has been demonstrated to improve the performance of infrared photodetectors. However, the successful experimental realization of the incorporation of such optical engineering structure into HgCdTe-based photodetectors has rarely been reported. In this paper, we present a HgCdTe infrared photodetector with integrated plasmonic structure. The experimental results show that the device with plasmonic structure has a distinct narrowband effect with a peak response rate close to 2 A/W, which is nearly 34% higher compared with the reference device. The simulation results are in good agreement with the experiment, and an analysis of the effect of the plasmonic structure is given, demonstrating the crucial role of the plasmonic structure in the enhancement of the device performance.

Plasmonic nanotechnology for photothermal applications - an evaluation

The application of plasmonic nanoparticles is motivated by the phenomenon of surface plasmon resonance. Owing to the tunability of optothermal properties and enhanced stability, these nanostructures show a wide range of applications in optical sensors, steam generation, water desalination, thermal energy storage, and biomedical applications such as photothermal (PT) therapy. The PT effect, that is, the conversion of absorbed light to heat by these particles, has led to thriving research regarding the utilization of plasmonic nanoparticles for a myriad of applications. The design of conventional nanomaterials for PT conversion has focussed predominantly on the manipulation of photon absorption through bandgap engineering, doping, incorporation, and modification of suitable matrix materials. Plasmonic nanomaterials offer an alternative and attractive approach in this regard, through the flexibility in the excitation of surface plasmons. Specific advantages are the considerable improved bandwidth of the absorption, a higher efficiency of photon absorption, facile tuning, as well as flexibility in the synthesis of plasmonic nanomaterials. This review of plasmonic PT (PPT) research begins with a theoretical discussion on the plasmonic properties of nanoparticles by means of the quasi-static approximation, Mie theory, Gans theory, generic simulations on common plasmonic material morphologies, and the evaluation processes of PT performance. Further, a variety of nanomaterials and material classes that have potential for PPT conversion are elucidated, such as plasmonic metals, bimetals, and metal-metal oxide nanocomposites. A detailed investigation of the essential, but often ignored, concept of thermal, chemical, and aggregation stability of nanoparticles is another part of this review. The challenges that remain, as well as prospective directions and chemistries, regarding nanomaterials for PT conversion are pondered on in the final section of the article, taking into account the specific requirements from different applications.

Active Site Engineering on Plasmonic Nanostructures for Efficient Photocatalysis

Plasmonic nanostructures have shown immense potential in photocatalysis because of their distinct photochemical properties associated with tunable photoresponses and strong light-matter interactions. The introduction of highly active sites is essential to fully exploit the potential of plasmonic nanostructures in photocatalysis, considering the inferior intrinsic activities of typical plasmonic metals. This review focuses on active site-engineered plasmonic nanostructures with enhanced photocatalytic performance, wherein the active sites are classified into four types (i.e., metallic sites, defect sites, ligand-grafted sites, and interface sites). The synergy between active sites and plasmonic nanostructures in photocatalysis is discussed in detail after briefly introducing the material synthesis and characterization methods. Active sites can promote the coupling of solar energy harvested by plasmonic metal to catalytic reactions in the form of local electromagnetic fields, hot carriers, and photothermal heating. Moreover, efficient energy coupling potentially regulates the reaction pathway by facilitating the excited state formation of reactants, changing the status of active sites, and creating additional active sites using photoexcited plasmonic metals. Afterward, the application of active site-engineered plasmonic nanostructures in emerging photocatalytic reactions is summarized. Finally, a summary and perspective of the existing challenges and future opportunities are presented. This review aims to deliver some insights into plasmonic photocatalysis from the perspective of active sites, expediting the discovery of high-performance plasmonic photocatalysts.

SiO2@Au nanoshell-assisted laser desorption/ionization mass spectrometry for coronary heart disease diagnosis

Cardiovascular diseases have threatened human health, amongst which coronary heart disease (CHD) is the third most common cause of death. CHD is considered to be a metabolic disease; however, there is little research on the CHD metabolism. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has enabled the development of a suitable nanomaterial that can be used to obtain considerable high-quality metabolic information without complex pretreatment of biological fluid samples. This study combines SiO₂@Au nanoshells with minute plasma to obtain metabolic fingerprints of CHD. The thickness of the SiO₂@Au shell was also optimized to maximize the laser desorption/ionization effect. The results demonstrated 84% sensitivity at 85% specificity for distinguishing CHD patients from controls in the validation cohort.

Tailored Dispersion of Spectro-Temporal Dynamics in Hot-Carrier Plasmonics

Ultrafast optical switching in plasmonic platforms relies on the third-order Kerr nonlinearity, which is tightly linked to the dynamics of hot carriers in nanostructured metals. Although extensively utilized, a fundamental understanding on the dependence of the switching dynamics upon optical resonances has often been overlooked. Here, all-optical control of resonance bands in a hybrid photonic-plasmonic crystal is employed as an empowering technique for probing the resonance-dependent switching dynamics upon hot carrier formation. Differential optical transmission measurements reveal an enhanced switching performance near the anti-crossing point arising from strong coupling between local and nonlocal resonance modes. Furthermore, entangled with hot-carrier dynamics, the nonlinear correspondence between optical resonances and refractive index change results in tailorable dispersion of recovery speeds which can notably deviate from the characteristic lifetime of hot carriers. The comprehensive understanding provides new protocols for optically characterizing hot-carrier dynamics and optimizing resonance-based all-optical switches for operations across the visible spectrum.

Observation of Multi-Directional Energy Transfer in a Hybrid Plasmonic-Excitonic Nanostructure

Hybrid plasmonic devices involve a nanostructured metal supporting localized surface plasmons to amplify light-matter interaction, and a non-plasmonic material to functionalize charge excitations. Application-relevant epitaxial heterostructures, however, give rise to ballistic ultrafast dynamics that challenge the conventional semiclassical understanding of unidirectional nanometal-to-substrate energy transfer. Epitaxial Au nanoislands are studied on WSe₂ with time- and angle-resolved photoemission spectroscopy and femtosecond electron diffraction: this combination of techniques resolves material, energy, and momentum of charge-carriers and phonons excited in the heterostructure. A strong non-linear plasmon-exciton interaction that transfers the energy of sub-bandgap photons very efficiently to the semiconductor is observed, leaving the metal cold until non-radiative exciton recombination heats the nanoparticles on hundreds of femtoseconds timescales. The results resolve a multi-directional energy exchange on timescales shorter than the electronic thermalization of the nanometal. Electron-phonon coupling and diffusive charge-transfer determine the subsequent energy flow. This complex dynamics opens perspectives for optoelectronic and photocatalytic applications, while providing a constraining experimental testbed for state-of-the-art modelling.

Plasmonic Photocatalysis for CO2 Reduction: Advances, Understanding and Possibilities

Plasmonic photocatalysis for CO₂ reduction is attracting increasing attention due to appealing properties and great potential for real applications. In this review, the fundamentals of plasmonic photocatalysis and the most recent developments regarding its application in driving CO₂ reduction are reported. Firstly, we present the review on the mechanism of plasmonic photocatalytic CO₂ reduction, the energy transfer of plasmon, and the CO₂ reduction process on the catalyst surface. Then, the modulation on the plasmonic nanostructures and also the semiconductor counterpart to regulate CO₂ photoreduction is discussed. Next, the influence of the core-shell structure and the interface between the plasmonic metal and semiconductor on the CO₂ photoreduction performance is also outlined. In addition, the latest progress on the emerging direction regarding the plasmonic photocatalysis for methane dry reforming with CO₂ is especially emphasized. Finally, a summary on the challenges and prospects of this promising field are provided.

Exploiting the LSPR effect for an enhanced photocatalytic hydrogen evolution reaction

Incorporation of plasmonic metals is one of the most widely adopted strategies for improving the photocatalytic hydrogen evolution reaction (HER) activity of semiconductor photocatalysts. This article summarizes recent advances in the development of plasmonic metal-semiconductor photocatalysts and four localized surface plasmon resonance (LSPR) driven mechanisms by which plasmonic metal nanoparticles can contribute to enhancement of HER activity. In addition, principles for maximizing the contribution of these LSPR driven mechanisms are highlighted to provide insights for future design of plasmonic metal-semiconductor photocatalysts with enhanced HER activity.

Effect of surface roughness on the solar evaporation of liquid marbles

HYPOTHESIS

Nanostructured materials are widely used for solar energy harvesting and conversion due to their excellent photothermal properties. It is generally accepted that the better the light absorption ability, the better the photothermal conversion efficiency.

EXPERIMENT

A series of experiments in solar evaporation of liquid marbles (LMs) by coating the droplets with Fe3O4, Ni nanoparticles (NPs) and carbon nanotubes (CNTs) are conducted.

FINDINGS

Conversely, we found that the surface roughness of solar absorber plays a significant role in solar evaporation rather than the light absorption. The results disclose that the Fe3O4 NPs with the lowest absorptivity has the largest roughness on drop surface, while that of CNTs show the opposite properties. The evaporation dynamics of LMs are featured with dome or constant spherical collapse with different roughness. Such dynamic difference arises from the mechanical competition between the capillary force and interparticle interaction. Besides, the strong light-harvesting and near-field radiation enabled by the rough surfaces enhance the solar evaporation. The Fe3O4-LM shows the highest evaporation rate of 6.55 μg/s, which is 1.09 and 1.30 times larger than that of Ni-LM and CNT-LM, respectively. Numerical analysis reveals that the rough surface with stacking arrangement of NPs greatly enhances the light-induced electromagnetic field and heat concentration over the interface, leading to a plasmon-coupling boundary with high temperature for the fast evaporation. Uncovering these properties could be of much help for developments of heatable miniature evaporators or reactors and their counterparts, permitting a broad range of processes with precise temperature and kinetic control.

Effect of light at different wavelengths on polyol synthesis of silver nanocubes

Despite the presence of light-sensitive species in the polyol synthesis of silver nanocubes, the influence of light on it has yet to be investigated. Herein, we demonstrated that light radiation, by generating plasmon-based hot electrons and subsequently increasing the reduction rate of Ag⁺ in the system, in addition to enhancing the growth rate of nanocubes, causes twinned seeds, which these seeds are then converted into nanorods and right bipyramids. With shorter, higher energy wavelengths, Ag⁺ reduction progresses more quickly, resulting in structures with more twin planes. The overlap of the excitation wavelength and the band gap of Ag₂S clusters formed in the early stages of synthesis accelerates the rate of reaction at low-energy excitation. According to our findings, the surfactant polyvinylpyrrolidone acts as a photochemical relay to drive the growth of silver nanoparticles. Overall, this work emphasizes the impact of excitation light on polyol synthesis as a technique for generating Ag nanocubes of various sizes.