Plasmonic Nanoparticles

The aim of this simple, quick, and safe laboratory exercise is to provide undergraduate students an introduction to nanotechnology using nanoparticle (NP) synthesis. Students are provided two procedures that allow for the synthesis of different yet controlled sizes of silver NPs. After preparing the NPs, the students perform UV−visible spectroscopy and full-width-half-maximum (fwhm) analysis to determine the size of the NPs they have synthesized. In doing so, the students made nanoparticles of size ranges from 10− 100 nm, thus spanning the range of nanotechnology. The experiments are designed to be accomplished in a single 90 min session and have been successfully conducted with over 1000 first-year-level students over a three-year period.

In 1918 Albert Einstein wrote in a letter to Walter Dällenbach against his own theory of optical force: “It has long been known that the values I had derived with Laub at the time are wrong; Abraham, in particular, was the one who presented this in a thorough paper. The correct strain tensor has incidentally already been pointed out by Minkowski”. Unfortunately after almost 100 years, it is still not clear why Einstein wrote so regarding the theory of optical/electromagnetic force (the optical stress tensor (ST)) associated with Lorentz force. The electromagnetic force is one of the four fundamental interactions (other three: the strong interaction, the weak interaction and gravitation) in nature. In spite of experiencing much progress from 1970, research on optical/electromagnetic forces has so far revealed only the partial nature of light-matter interaction. For example, inside a material media an appropriate description of photon momenta (i.e. the Abraham-Minkowski dilemma) and an appropriate description of stress tensors along with Lorentz /volumetric forces (known as Minkowski, Abraham, Chu, Einstein-Laub and Ampere/Nelson forces) are still matters of great controversy. In this thesis, physics and applications of Lorentz force along with stress tensors and photon momenta have been investigated in details with special interest in tractor beam effect, plasmonic objects, chiral objects and the objects embedded in a generic material medium. At first, we have considered simpler case: application of Lorentz force for the objects placed in air. Specifically we demonstrate how the mechanism of Lorentz force can be used in a tractor beam-like effect for pulling multiple Rayleigh particles placed outside a dielectric hollow core waveguide and coupler. We also represent the Lorentz force analysis for plasmonic off-axis and on-axis spherical heterodimers and it is shown that the reversal of longitudinal binding force can be easily controlled by forced symmetry breaking. Though it is commonly believed that plasmonic forces mostly arise from the surface force and Fano resonance can be a promising way to achieve binding force reversal, our study based on Lorentz force dynamics suggests notably opposite proposals for the case of plasmonic spherical heterodimers. Next, we have also considered objects those are embedded in a material medium. The fundamental results/proposals of this thesis are presented afterwards. We have shown that the well-known Lorentz force leads to inconsistent result (pushing force) instead of the experimentally observed optical pulling force as observed in interfacial tractor beam experiments. As one of the major contributions of this thesis, we identify the ‘exact’ reasons why the well-known distinct Lorentz/volumetric forces fail not only for interfacial tractor beam experiment but also for several other major radiation pressure experiments performed up to date. Later, we demonstrate that it is still possible to establish different equivalent time-averaged Lorentz / volumetric force formulas based on the fulfilment of just two ‘consistency conditions’. Based on those proposed ‘consistency conditions’, finally, we demonstrate that by modifying the Einstein-Laub or Chu formulation; time-averaged STs and volume forces are obtainable, which can overcome the aforementioned inconsistencies. For example- these modified formulations can yield the ‘correct’ time averaged force similar to Minkowski’s force for almost all the previous real experiments. Specially, our proposed modified Einstein-Laub ST can be considered as an efficient mathematical toolkit, an alternative of time and memory consuming volumetric forces, to yield the internal bulk force of a chiral or achiral object embedded in complex material backgrounds (i.e. homogeneous, heterogeneous, bounded etc.). Later, we have also shown an interesting application of modified Lorentz force to control the reversal of optical binding force of plasmonic cubes placed over plasmonic substrate due to strong Fano resonance. Finally, based on our proposals throughout the thesis, at the end of this thesis we propose a new hypothesis named as the ‘existence domain’. ‘Existence domain’ is the region either outside of a scattering body taking only its exterior fields into account, or in its interior considering only the inside fields. Though almost all the time averaged distinct STs and volumetric force laws are restricted to the idea of ‘existence domain’, we demonstrate that the stress tensor, volumetric force and photon momentum of Minkowski are free from such and other restrictions both in instantaneous and time averaged situations. After almost 100 years of Einstein’s prediction, this thesis, most probably, finally answers why only Minkowski’s theory of optical force and photon momentum remains consistent in all circumstances. Proposals presented in this thesis can be very effective for resolving not only the dilemma of distinct stress tensors and optical Lorentz/ volumetric forces but also for settling the controversy of Abraham-Minkowski photon momenta. This thesis may also open a new window for optical pulling force/tractor beams along with the novel manipulation process of plasmonic dimers.

In this report a simple and eco-friendly biosynthesis of silver
nanoparticles using Pomegranate peel extract as the reducing agent
from 1 mM AgNO3 had been investigated. The formation of silver
nanoparticles was characterized by UV-Vis spectrum, Fourier
Transform Infrared Spectroscopy (FT-IR) and Scanning Electron
Microscopic (SEM) analysis. The UV-Vis spectra results show a
strong resonance centered on the surface of silver nanoparticles
(AgNPs) at 371 nm. The Fourier Transformation Infrared
Spectroscopy spectral study demonstrates pomegranate peel extract
acted as the reducing agent. The scanning electron microscopic
(SEM) analysis shows nanoparticles with the average particles size
ranges about 5-50 nm. Further the antibacterial activity of AgNPs
was evaluated against Staphylococcus aureus, Pseudomonas
aeruginosa and Escherichia coli pathogens. This route is rapid,
simple, without any hazardous chemicals as reducing or stabilizing
agents and economical to synthesize AgNPs.

Dye sensitized solar cells (DSSCs) have numerous advantages, but in order to use widespread industrial deployment we need to boost the power conversion efficiency. One promising approach to improve DSSC performance is to improve the spectral response of sensitizers with metal nanoparticle-based surface plasmon resonance. Even single shaped nanoparticles (NPs), however, have physical limitations. Thus, in this study a simple synthesis route is used to fabricate multishaped silver (Ag) NPs to create a coupled plasmonic effect in DSSC to cover more of the solar spectrum. The impact of multishaped AgNPs combinations are studied to determine which aspects improve the power conversion efficiency of DSSC. A detailed investigation was made of both the TiO2 (XRD) and AgNPs (UV-Vis spectrometry) to couple the impacts on the DSSC (I-V) with the combination of the morphologies (TEM and FESEM) of AgNPs. Synthesized AgNPs with distinct extinction cross section covers the visible and IR regime from 300 nm to 1100 nm by tuning its plasmonics band. It is inferred that multi-shaped AgNPs predominately enhance the light harvesting, charge separation and carrier transportation. The results show that the increment in short circuit current and open circuit voltage resulted in an increase of 45% overall power conversion efficiency in the standard DSSC device is attributed to the usage of multi-shaped AgNPs. Finally, a mechanism is proposed to support the outcome of the experiment by demonstrating the extinction cross section and the local field of the various shaped AgNPs using Finite-difference time-domain (FDTD) simulation.

ARTICLE scitation.org/journal/adv Comparative study of thermoplasmonic effects of gold and silver metal nanoparticle ABSTRACT We investigated the plasmonic heating effect of noble metal nanoparticles in a water environment using the first-principles approach. In this approach, we have solved the heat transfer equation in the steady state to obtain the heat generation and temperature profile corresponding to two different types of metals. Metals exhibited a surface plasmon resonance property in which maximum absorption of light for smaller size nanoparticles is observed, which can be used to heat up the surrounding environment. Inspired by the same, we have simulated the absorption cross section of different sizes of a metal nanosphere and observed the threshold value of the radius below which absorption is dominant. The maximum absorption of light by the nanosphere produces a hotspot, which can be visualized in terms of the electric field distribution plot. This electric field distribution profile of silver and gold metal nanoparticles is computed under the resonance wavelength using the boundary element method The results thus obtained in terms of the optical cross section are compared with those of the numerical model to establish their veracity. These theoretical works aim to further develop the fundamental understanding of the heating mechanism of plasmonic geometries, which can be used in several applications.

Cathodoluminescence (CL) is a powerful tool for the investigation of optical properties of materials. In recent years, its combination with scanning transmission electron microscopy (STEM) has demonstrated great success in unveiling new physics in the field of plasmonics and quantum emitters. Most of these results were not imaginable even twenty years ago, due to conceptual and technical limitations. The purpose of this review is to present the recent advances that broke these limitations, and the new possibilities offered by the modern STEM-CL technique. We first introduce the different STEM-CL operating modes and the technical specificities in STEM-CL instrumentation. Two main classes of optical excitations, namely the coherent one (typically plasmons) and the incoherent one (typically light emission from quantum emitters) are investigated with STEM-CL. For these two main classes, we describe both the physics of light production under electron beam irradiation and the physical basis for interpreting STEM-CL experiments. We then compare STEM-CL with its better known sister techniques: scanning electron microscope CL, photoluminescence, and electron energy-loss spectroscopy. We finish by comprehensively reviewing recent STEM-CL applications.

SiO2 and TiO2 thin films with gold nanoparticles (NPs) are of particular interest as photovoltaic materials. A novel method for the preparation of spin-coated SiO2–Au and TiO2–Au nanocomposites is presented. This fast and inexpensive method, which includes three separate stages, is based on the in situ synthesis of both the metal-oxide matrix and the Au NPs during a baking process at relatively low temperature. It allows the formation of nanocomposite thin films with a higher concentration of Au NPs than other methods. High-resolution transmission electron microscopy studies revealed a homogeneous distribution of NPs over the film volume along with their narrow size distribution. The optical manifestation of localized surface plasmon resonance was studied in more detail for TiO2-based Au-doped nanocomposite films deposited on glass (in absorption and transmittance) and silicon (in specular reflectance). Maxwell–Garnett effective-medium theory applied to such metal-doped nanocomposite films describes the peculiarities of the experimental spectra, including modification of the antireflective properties of bare TiO2 films deposited on silicon by varying the concentration of metal NPs. The antireflective capabilities of the film are increased after a wet etching process.

Upconversion (UC) of lanthanide-doped nanostructure has the unique ability to convert low energy infrared (IR) light to high energy photons, which has significant potential for energy conversion applications. This review concisely discusses the basic concepts and fundamental theories of lanthanide nanostructures, synthesis techniques, and enhancement methods of upconversion for photovoltaic and for near-infrared (NIR) photodetector (PD) application. In addition, a few examples of lanthanide-doped nanostructures with improved performance were discussed, with particular emphasis on upconversion emission enhancement using coupling plasmon. The use of UC materials has been shown to significantly improve the NIR lightharvesting properties of photovoltaic devices and photocatalytic materials. However, the inefficiency of UC emission also prompted the need for additional modification of the optical properties of UC material. This improvement entailed the proper selection of the host matrix and optimization of the sensitizer and activator concentrations, followed by subjecting the UC material to surface-passivation, plasmonic enhancement, or doping. As expected, improving the optical properties of UC materials can lead to enhanced efficiency of PDs and photovoltaic devices.

Recent advances in the use of plasmonic metamaterials to improve absorption of light in thin-film solar photovoltaic devices has created a demand for a scalable method of patterning large areas with metal nanostructures deposited in an ordered array. This article describes two methods of fabricating ordered 2D nanosphere colloidal films: spin coating and interface coating. The two methods are compared and parameter optimization discussed. The study reveals that: For smaller nanosphere sizes, spin coating is more favorable, while for larger nanospheres, the angled interface coating provides more coverage and uniformity. A surfactant-free approach for interface coating is developed to fabricate zero-contamination colloidal films. Each of the methods reaches an overall coverage of more than 90% and can be used for nanosphere lithography to form plasmonic metamaterials.

It is theoretically shown that a thin composite slab comprised of a transparent host and uniformly oriented disc-like silver nanoparticles deposited onto a glass surface can act as an anti-reflection coating. The applicability of the effective-medium model for describing the optical properties of thin heterogeneous layers with moderate volume fraction of inclusions is verified using full-wave finite-element simulations.

Bimetallic plasmonic nanoparticles enable tuning of the optical response and chemical stability by variation of the composition. The present numerical simulation study compares Ag−Au alloy, Ag@Au core−shell, and Au@Ag core−shell bimetallic plasmonic nanoparticles of both spherical and anisotropic (nanotriangle and nanorods) shapes. By studying both spherical and anisotropic (with LSPR in the near-infrared region) shapes, cases with and without interband transitions of Au can be decoupled. Explicit comparisons are facilitated by numerical models supported by careful validation and examination of optical constants of Au−Ag alloys reported in the literature. Although both Au−Ag core−shell and alloy nanoparticles exhibit an intermediary optical response between that of pure Ag and Au nanoparticles, there are noticeable differences in the spectral characteristics. Also, the effect of the bimetallic constitution in anisotropic nanoparticles is starkly different from that in spherical nanoparticles due to the absence of Au interband transitions in the former case. In general, the improved chemical stability of Ag nanoparticles by incorporation of Au comes with a cost of reduction in plasmonic enhancement, also applicable to anisotropic nanoparticles with a weaker effect. A photothermal heat transfer study confirms that increased absorption by the incorporation of Au in spherical Ag nanoparticles also results in an increased steady-state temperature. On the other hand, anisotropic nanoparticles are inherently better absorbers and hence better photothermal sources, and their photothermal properties are apparently not strongly affected by the incorporation of one metal in the other. This study of the optical/spectral and photothermal characteristics of bimetallic Au−Ag alloy versus core−shell nanoparticles provides detailed physical insight for development of new taylor-made plasmonic nanostructures.

This paper presents a novel design for the top contact of thin film photovoltaic (PV) solar cells. The new top contact is formed by fabricating a 20nm thin honeycomb shaped silver mesh on top of an ultra-thin 13nm of indium tin oxide. The new top contact offers the potential to reduce the series resistance of the cell while increasing the light current via plasmonic resonance. Using the nano-bead lithography technique the honeycomb top contact was fabricated and electrically characterized. The experimental results verified the new contact reduces the sheet resistance by about 40%. Numerical simulations were then used to analyze the potential performance enhancement in the cell. The results suggest the proposed top contact integrated with a typical thin film hydrogenated amorphous silicon PV device would lead to more than an 8% improvement in the overall efficiency of the cell.

Remote control of the pH of the medium is an important task for many applications in chemistry, medicine, and biology. Remote control of the pH using light is an intelligent and cost-effective approach. The nanoscale plasmon−exciton (plexciton) light−matter coupling is a physical phenomenon that provokes strong changes in the optical properties of the original plasmon and exciton bands, resulting in a transparency dip in the initial plasmon spectrum and formation of two hybrid plexciton side bands separated by the Rabi splitting energy. The plexciton coupling strength is unaffected by the temperature and light irradiation stressors but strongly depends on the transition dipole moment of the exciton material. Here, we show that the optical parameters of the plexciton coupling can be controlled by varying the pH of the medium. To demonstrate this, we obtained resonant light−matter coupling between the plasmon band of silver nanoplates and the J-band of J-aggregates with a Rabi splitting energy of up to 450 meV and found that both the extinction dip and the splitting energy are strongly affected by variation of pH from 2.5 to 11. We explain this effect by a change in the structure of the J-aggregates and reduction of the J-band intensity, which is confirmed by numerical simulation.

Photonics is considered as a major technological sector which plays a role in addressing many of the industrial and societal challenges faced globally today in : food, transport, media and communications, defence, manufacturing and production, construction, healthcare, environment and ICT. Photonics can be defined as the science of the light (photon) generation, detection, and manipulation.

Light can only be focused to a spot roughly half its wavelength in size (a few hundred nanometres for visible light). This limit is a challenge for many applications in photonics at the nanoscale (sensing and imaging systems, screens and displays, data transmission and storage, photovoltaics,…).

This limit can be surpassed by coupling light to electrons at the surface of a metal surface or a metal nanostructure and creating surface plasmons which enable strong light confinement and enhancement. Plasmonics is dedicated to the study of the coupling of light to the oscillation of free electrons in metals surfaces and metal nanostructures which creates surface plasmons.

Analysis of patent activity is crucial for industrial and commercial development in plasmonics area but there is no patent landscape report currently available focused on Plasmonics.

This report provides a long-term overview of the patent landscape in Plasmonics. The report includes a cross statistic analysis from 1996 to 2016 :
- by publication countries
- by industrial and academic applicants
- by application segments
- by industrial key applicants
This 130 pages report contains around 190 figures and 30 tables.

The main aim of this study is to scrutinize promising plasmonic materials by understanding their electronic structure and correlating them to the optical properties of selected refractory materials. For this purpose, the electronic and optical properties of the conductive ceramics TiC, ZrC, HfC, TaC, WC, TiN, ZrN, HfN, TaN, and WN are studied systematically by means of first-principles density functional theory. A full ab initio procedure to calculate plasma frequency from the electronic band structure is discussed. The dielectric functions are calculated by including electronic interband and intraband transitions. Our calculations confirm that transition metal nitrides, such as TiN, ZrN, and HfN, are the strongest candidates, exhibiting performance comparable to that of conventional noble metals in the visible to the near-infrared regions. On the other hand, carbides are not suitable for plasmonic applications because they show very large losses in the same regions. From our calculated dielectric functions, the scattering and absorption efficiencies of nanoparticles made of these refractory materials are evaluated. It is revealed that TiN and TaC are the best candidate materials for applications in photothermal energy conversion over a broad spectral region. Furthermore, quality factors for localized surface plasmon resonance and surface plasmon polaritons are calculated to compare quantitative performances, and ZrN and HfN are found to be comparable to conventional plasmonic metals such as silver and gold.

Plasmonic metasurfaces are promising as enablers of nanoscale nonlinear optics and flat nonlinear optical components. Nonlinear optical responses of such metasurfaces are determined by the nonlinear optical properties of individual plasmonic meta-atoms. Unfortunately, no simple methods exist to determine the nonlinear optical properties (hyperpolarizabilities) of the meta-atoms hindering the design of nonlinear metasurfaces. Here, we develop the equivalent RLC circuit (resistor, inductor, capacitor) model of such meta-atoms to estimate their second-order nonlinear optical properties, that is, the first-order hyperpolarizability in the optical spectral range. In parallel, we extract from second-harmonic generation experiments the first-order hyperpolarizabilities of individual meta-atoms consisting of asymmetrically shaped (elongated) plasmonic nanoprisms, verified with detailed calculations using both nonlinear hydrodynamic-FDTD and nonlinear scattering theory. All three approaches, analytical, experimental, and computational, yield results that agree very well. Our empirical RLC model can thus be used as a simple tool to enable an efficient design of nonlinear plasmonic metasurfaces. P hotonic metamaterials are artificial structures exhibiting optical properties that in natural materials are either very weak or entirely lacking. Among these properties are phase mismatched light-propagation, optical magnetism, strong chirality, and epsilon-near-zero behavior. 1−5 There is a growing interest in understanding and harnessing the nonlinear optical responses of metasurfaces. 6−14 Many photonic applications including frequency conversion, THz generation, photon-pair generation, ultrashort-pulse generation, frequency-comb generation , and all-optical switching 15−19 rely on nonlinear optics occurring in large bulky devices where one must contend with phase mismatching. In contrast, the small footprint of metasurfaces virtually guarantees phase matching, and moreover , the nonlinear emission can be precisely controlled. 2,3,20,21 Plasmonic metasurfaces have recently emerged as a promising candidate for enabling nanoscale nonlinear optics. 6 The optical responses of plasmonic meta-atoms serving as unit cells of metasurfaces are dictated by the collective movement of the conduction electrons giving rise to localized surface plasmons (LSPs). Therefore, it is imperative to investigate the conduction electron dynamics and the nonlinear response of the constituting meta-atoms. Such investigations can be performed, for example, by using the hydrodynamic plasma model 22−25 and the nonlinear scattering theory. 26 However, relying on computational tools is not always convenient due to their complexity and the large amount of computational resources they often require. Linear and nonlinear optical responses of plasmonic meta-atoms can also be predicted by equivalent RLC circuit (resistor, inductor, capacitor) theory. 27−31 This approach has correctly described the nonlinear and magnetic responses of split-ring resonators operating at microwave frequencies. 32 Nevertheless, it remained unclear whether the RLC approach could describe conduction electron dynamics in plasmonic meta-atoms adequately enough to accurately predict their nonlinear responses at optical wavelengths as well. In this Letter, we derive the first-order hyperpolarizability of individual plasmonic meta-atoms by adapting the equivalent RLC model that we find can, indeed, be used to predict collective second-order nonlinear responses of large meta-surfaces. First, we derive an expression for the first-order hyperpolarizability with an unknown nonlinear coefficient a that represents the strength of the nonlinear charge oscillation in an individual meta-atom. Our goal is to determine the value of a through physical arguments and to validate our approach through rigorous experiments and numerical calculations. Next, we describe our second-harmonic generation (SHG) experiments, where we measured SHG emission from metasurfaces consisting of randomly arranged gold elongated nanoprisms. From these measurements, we extract the

Assemblies of closely separated gold nanoparticles exhibit a strong collective plasmonic response due to coupling of the plasmon modes of the individual nanostructures. In the context of self-assembly of nanoparticles, close-packed two-dimensional (2D) clusters of spherical nanoparticles present an important composite system that promises numerous applications. The present study probes the collective plasmonic characteristics and resulting photothermal behavior of close-packed 2D Au nanoparticle clusters to delineate the effects of the cluster size, interparticle distance, and particle size. Smaller nanoparticles (20 and 40 nm in diameter) that exhibit low individual scattering and high absorption were considered for their relevance to photothermal applications. In contrast to typical literature studies, the present study compares the optical response of clusters of different sizes ranging from a single nanoparticle up to large assemblies of 61 nanoparticles. Increasing the cluster size induces significant changes to the spectral position and optophysical characteristics. Based on the model outcome, an optimal cluster size for maximum absorption per nanoparticle is also determined for enhanced photothermal effects. The effect of the particle size and interparticle distance is investigated to elucidate the nature of interaction in terms of near-field and far-field coupling. The photothermal effect resulting from absorption is compared for different cluster sizes and interparticle distances considering a homogeneous water medium. A strong dependence of the steady-state temperature of the nanoparticles on the cluster size, particle position in the cluster, incident light polarization, and interparticle distance provides new physical insight into the local temperature control of plasmonic nanostructures.

Defects may tend to make crystals interesting but they do not always improve performance. In doped metal oxide nanocrystals with localized surface plasmon resonance (LSPR), aliovalent dopants and oxygen vacancies act as centers for ionized impurity scattering of electrons. Such electronic damping leads to lossy, broadband LSPR with low quality factors, limiting applications that require near-field concentration of light. However, the appropriate dopant can mitigate ionized impurity scattering. Herein, we report the synthesis and characterization of a novel doped metal oxide nanocrystal material, cerium-doped indium oxide (Ce:In 2 O 3). Ce:In 2 O 3 nanocrystals display tunable mid-infrared LSPR with exceptionally narrow line widths and the highest quality factors observed for nanocrystals in this spectral region. Drude model fits to the spectra indicate that a drastic reduction in ionized impurity scattering is responsible for the enhanced quality factors, and high electronic mobilities reaching 33 cm 2 V −1 s −1 are measured optically, well above the optical mobility for tin-doped indium oxide (ITO) nanocrystals. We investigate the microscopic mechanisms underlying this enhanced mobility with density functional theory calculations, which suggest that scattering is reduced because cerium orbitals do not hybridize with the In orbitals that dominate the bottom of the conduction band. Ce doping may also reduce the equilibrium oxygen vacancy concentration, further enhancing mobility. From the absorption spectra of single Ce:In 2 O 3 nanocrystals, we determine the dielectric function and by simulation predict strong near-field enhancement of mid-IR light, especially around the vertices of our synthesized nanocubes. D oped metal oxide nanocrystals display intriguing composition-dependent properties. Chief among these is near-to mid-infrared (NIR/MIR) localized surface plasmon resonance (LSPR), which is induced by n-type doping to generate free electrons that can participate in light-driven free carrier oscillation at tunable resonant frequencies. Colloidal synthesis has enabled the discovery of several doped metal oxide nanocrystals with LSPR over the past decade. Key examples include aluminum-doped zinc oxide (AZO), 1 indium-doped cadmium oxide (ICO), 2 and tin-doped indium oxide (ITO or Sn:In 2 O 3). 3 These materials have been studied as thin films for their transparent conductive properties, and the dielectric functions known from such studies are the basis for understanding the LSPR properties of the corresponding nanocrystals. LSPR excitations are confined to the physical dimensions of nanocrystals and effectively concentrate light into volumes well below the diffraction limit. As a result, very intense local field " hotspots " are formed around the nanocrystals that can interact with nearby molecules or materials. This near-field enhancement makes doped metal oxide nanocrystals good candidates for NIR and MIR near-field optics and enhanced spectroscopies like surface-enhanced infrared absorption spectroscopy (SEIRA). Efficient hot spot generation requires a high quality factor (Q, the ratio of the peak energy to the width of the LSPR peak), which implies longer plasmon lifetimes, weaker electronic damping, and stronger near-field intensities. Thus, it is important to consider not only how dopants in metal oxides tune the LSPR frequency by changing the free carrier concentration but also how their presence contributes to damping by scattering the oscillating free electrons. To create high-Q MIR plasmonic materials, strategies are needed to minimize scattering even as substantial concentrations of dopants are introduced. To account for both free carrier concentration and electronic damping, the dielectric function of a doped oxide nanocrystal can be represented by the Drude model extended to include a frequency-dependent contribution to the damping of oscillating free carriers

Reliable control of spontaneous radiation from quantum emitters, such as quantum dots (QDs), is an extremely important problem in quantum science, nanophotonics, and engineering. The QD photoluminescence (PL) may be enhanced near plasmon nanoparticles because of excitation field enhancement or the Purcell effect. However, both of these effects have their specific limitations. The excitation enhancement is usually accompanied by a decrease in the PL quantum yield (QY) due to the plasmon-induced energy transfer, and the Purcell effect cannot significantly enhance the PL of QDs with an initially high QY because of the obvious limitation of the QY by the value of 100%. Here, we have shown that the synergistic combination of excitation enhancement caused by silver nanospheres and the Purcell effect caused by silver nanoplates in the same QD-in-polymer hybrid thin-film nanostructure permits simultaneous increases in the radiative and excitation rates to be obtained. This overcomes the limitations of each individual effect and yields a synergistic PL increase (+1320%) greater than the sum of the PL enhancements determined by each effect alone (+70% and +360%).

A uniformly dispersed Pd/Ag bimetallic system supported on mesoporous silica SBA-15 was synthesized by a two-step method. Ag/SBA-15 was first synthesized by the microwave-assisted alcohol reduction method, which afforded color-controlled Ag nanoparticles (NPs) with different particle sizes and morphologies. Among them, the smaller yellowish Ag NPs exhibited the highest catalytic activity in H 2 production from ammonia borane (NH 3 BH 3) under dark conditions, while the maximum enhancement under visible light irradiation was attained by blue Ag nanorods. Further decoration of Ag/SBA-15 with Pd NPs was achieved via localized surface plasmon resonance (LSPR)-assisted deposition under visible light irradiation. All Pd/Ag/ SBA-15 catalysts showed higher catalytic activities than the inherent Ag/SBA-15 catalysts under both dark and visible-light irradiation conditions, where the Pd/Ag/SBA-15 originated from blue Ag nanorods afforded a maximum enhancement effect. The order of increasing catalytic activity was found to be in accordance with the Ag-LSPR absorption intensity. The LSPR-enhanced photocatalytic activity of the Pd/Ag/SBA-15 was also demonstrated in the Pd-driven Suzuki–Miyaura coupling reaction of aryl halides with boronic acids, where a similar trend in the enhancement of catalytic activity was observed under visible light irradiation.

We experimentally and theoretically investigate the interactions between localized plasmons in gold nanorods and excitons in J-aggregates under ambient conditions. Thanks to our sample preparation procedure we are able to track a clear anticrossing behavior of the hybridized modes not only in the extinction but also in the photoluminescence (PL) spectra of this hybrid system. Notably, while previous studies often found the PL signal to be dominated by a single mode (emission from so-called lower polariton branch), here we follow the evolution of the two PL peaks as the plasmon energy is detuned from the excitonic resonance. Both the extinction and PL results are in good agreement with the theoretical predictions obtained for a model that assumes two interacting modes with a ratio between the coupling strength and the plasmonic losses close to 0.4, indicative of the strong coupling regime with a significant Rabi splitting estimated to be ∼200 meV. The evolution of the PL line shape as the plasmon is detuned depends on the illumination wavelength, which we attribute to an incoherent excitation given by decay processes in either the metallic rods or the J-aggregates.

The spectral characteristics of a one-dimensional photonic crystal with an inset made of a heterogeneous composite material containing metal nanoparticles of different sizes have been studied. The influence of the size-dependent relative permittivity of nanoparticles on the spectrum of the photonic crystal has been demonstrated.

The photoconversion of photomorphic silver nanoparticles from
discs to prisms via citrate mediated growth on the twin plane
faces of the nanoparticles is demonstrated. This systematic
shape evolution from discs to hexagons and then prisms of
increasing aspect ratios is a result of the growth process being
confined to specific faces of the growing nanoparticles.

This paper examines the key features of the transmission and reflection spectra of a one-dimensional photonic crystal structure in which a nanocomposite layer is sandwiched between dielectric Bragg mirrors. Two orthogonal polarisations of an incident wave correspond to different plasmon resonance frequencies of the nanocomposite. If one of the plasmon frequencies coincides with the defect mode frequency in one of the photonic bandgaps, complete suppression of the defect mode in the transmission spectrum is possible, which makes the spectra of such structures polarisation-sensitive.

One-dimensional wires are known to be inherently unstable at finite temperature. Here, we show that long-range order of atomic Au double chains adsorbed on a Si(553) surface is not only stabilized by interaction with the substrate, but spontaneous self-healing of structural defects is actually enforced by the adsorption of atomic species such as Au or H. This is true even for random adsorbate distribution. Combining atomistic models within density functional theory with low energy electron diffraction and high-resolution electron energy loss spectroscopy, we demonstrate that this apparently counterintuitive behavior is mainly caused by adsorption-induced band filling of modified surface bands, i.e., by the strong electronic correlation throughout the whole terrace. Although adsorption preferably occurs at the step edge, it enhances the dimerization and the stiffness of the Au dimers. Thus, the intertwinement of quasi-1D properties with delocalized 2D effects enforces the atomic wire order. The reduction of size and dimensionality of metallic objects gives rise to peculiar physical properties such as quantization of conductance, spin-charge separation, charge and spin density waves, and Luttinger liquid behavior [1-5], which are subject of fundamental studies on low-dimensional physics. Unfortunately, free-standing metallic wires cannot be realized due to their inherent instability [5]. This problem can be partially circumvented by the formation of self-assembled, metallic atomic chains on stepped semiconductor surfaces such as Ge and Si, which are regarded as the low-end limit for long-range ordered nano-structures [6-15]. Several realizations of such wire systems have been reported [11,16-21]. While structural embedding is a prerequisite for the realization of 1D wires, the coupling to higher dimensions implies an intricate balance between preservation and destruction of typical 1D instabilities [22]. On the other hand, the coupling to higher dimensions can be exploited to tune wire properties such as morphology and conductivity. Here, we demonstrate a quite unique and unexpected example thereof: the enhanced and even enforced order of atomic chains by random adsorption of atoms, as a new mechanism of crossover between 1D and 2D properties. This behavior is in striking contrast to previously investigated adsorbates, which adsorb at random for low concentrations and thus introduce disorder. While an increased order might be expected if the adsorbates build patterns with the same periodicity of existing structures on the surface, it appears counterintuitive as a consequence of randomly distributed adatoms. Among the metallic wires grown on regularly stepped surfaces, the Si(553)-Au is one of the most studied systems, due to its relatively high stability, and because of a long-standing debate concerning its exact atomic structure [11,18,19,23-27]. It is commonly accepted that the system features a Si honeycomb and a Au double chain on each terrace. The Au chain is dimerized (even in the absence of adsorbates), which leads to a ×2 periodicity along the terraces. Several attempts to tune the conductivity of this system by deposition of oxygen [28,29] or hydrogen [30-32] are available in the literature. They demonstrate an intricate scenario with adsorbate specific modifications of the electronic structure. Generally, different adsorption sites of similar energy are available on the surface, leading to a random adsorbate distribution and a complex modification of the electronic structure. In this Letter, we demonstrate the improvement of the dimerized Au chain order simply by adsorption of small amounts of surplus Au, or of atomic H at room temperature. Since these adsorbates, as shown in the following, adsorb at random sites, this effect does not depend on the formation of ordered adsorbate arrays. Density functional theory (DFT) calculations show that the observed behavior stems from the coupling of the 1D atomic chains to higher dimensions. The electronic structure is modified by the effective electron donation from the adsorbates. The latter affects nonlocally the atomic arrangement of the whole terrace, demonstrating the extreme electronic correlation in this quasi-1D system. The rearranged structure is by far less PHYSICAL REVIEW LETTERS 126, 106101 (2021)

ZnS nanoparticles have been synthesized by the facile chemical route with a narrow size distribution in the MA/octene-1 copolymer matrix and effect of reaction time has been discussed. X-ray diffraction pattern confirms the pure cubic phase of ZnS with 5-7 nm average crystal sizes which are in good agreement with the AFM and UV-Vis measurements. Absorption spectra exhibit a strong blue shift from the bulk with the 3.98 eV optical band gap which clearly indicates the strong size confinement effect. Thermogravimetric analyses show increased thermal stability of the nanocomposite compared to the copolymer. The possible growth mechanism of the particles formation and stabilization has been discussed.

Titanium dioxide exists in a large number of polymorphs, the most common ones being, in order of abundance, rutile, anatase and brookite. Recently, there has been an increasing degree of attention on TiO2 , due to its photocatalytic and antibacterial properties. In this work, titania nanopowders synthesized via an aqueous sol–gel method were modified with silver and/or tungsten, with potential application as photocatalysts and antibacterial agents. The dried gels were thermally treated at two temperatures, and the occurrence of amorphous phase—in both dried and calcined gels—was obtained using the Rietveld method. In powders calcined at 600 °C, the crystal structure of rutile was determined with the Rietveld method on the full profile fitting of the X-ray powder diffraction patterns, while microstructural information was achieved by means of Williamson–Hall plots and line broadening analysis methods. The photochromic property of the Ag and W/Ag modified samples—when subjected to both UV-and visible-light irradiation and for different time expo-sures—was also investigated via UV–Vis spectroscopy. Powders were shown to possess a tuneable photochromism due to the surface plasmon resonance of the added silver, depending on the firing temperature, light (and time) exposure, and on whether or not tungsten was present in the nanopowders.

Hybrid materials formed by plasmonic nanostructures and J-aggregates provide a unique combination of highly localized and enhanced electromagnetic field in metal constituent with large oscillator strength and extremely narrow exciton band of the organic component. The coherent coupling of localized plasmons of the multispiked gold nanoparticles (nanostars) and excitons of JC1 dye J-aggregates results in a Rabi splitting reaching 260 meV. Importantly, broad absorption features of nanostars extending over a visible and near-infrared spectral range allowed us to demonstrate double Rabi splitting resulting from the simultaneous coherent coupling between plasmons of the nanostars and excitons of J-aggregates of two different cyanine dyes.

We demonstrate modifications to the light yield properties of an organic liquid scintillator due to the localisation of the tertiary fluorophore component to the surface of Ag-core silica-shell nanoparticles. We attribute this enhancement to the near-field interaction of Ag nanoparticle plasmons with these fluor molecules. The scintillation light yield enhancement is shown to be equal to the fluorescence enhancement within measurement
uncertainties. With a suitable choice of plasmon energy and scintillation fluor, this effect may be used to engineer scintillators with enhanced light yields for radiation detection applications.