Localized Surface Plasmon Resonance Behavior Research Articles

Experimental and Theoretical Studies on Ag Nanoparticles with Enhanced Plasmonic Response, Formed Within Al2O3 Thin Films Deposited by Magnetron Sputtering

AbstractReactive magnetron sputtering was employed to prepare nanocomposite thin films of Ag/Al2O3, on a glass substrate. The films are characterized by the formation of Ag nanoparticles embedded in the Al2O3 matrix, after thermal treatment at 600 °C, which are responsible for the appearance of an outstanding pronounced and narrow localized surface plasmon resonance (LSPR) band. Electron microscopy analysis also revealed the presence of larger Ag fractal aggregates at the film’s surface, responsible for a broad band absorption. Noteworthily, the LSPR band maximum remains at the same position (about 412 nm) for Ag concentrations ranging from 23 to 34 at.%, despite some discernible alterations in both LSPR band intensity and width. An optimized thin film is characterized by full transparency in non-resonant wavelengths due to suppression of Ag aggregates at the film’s surface, while maintaining the LSPR behavior. To better explain the plasmonic behavior of the Ag/Al2O3 films, discrete dipole approximation was used to determine the extinction, scattering, and absorption efficiencies of Ag spheres surrounded by an Al2O3 cap layer. This allowed to ascertain some nanostructural features of the films, pointing to the formation of Ag nanoparticles with average sizes in the order of 40 nm.

Single-Particle Spectroelectrochemistry: Promoting the Electrocatalytic Activity of Gold Nanorods via Oxygen Plasma Treatment without Structural Deformation.

Understanding of the electrocatalytic activity enhancement in gold nanoparticles is still limited. Herein, we present the effect of the oxygen plasma treatment on the electrochemical activity of gold nanorods (AuNRs). Oxygen plasma treatment resulted in the blueshift and line width narrowing of the localized surface plasmon resonance (LSPR) spectra obtained from individual AuNRs immobilized on an indium tin oxide (ITO) surface. These changes can be attributed to increases in the surface charges of the AuNRs. The formation of a Au-ITO heterojunction provided structural stability to the immobilized AuNRs regardless of the duration of oxygen plasma exposure. The electrocatalytic oxidation of hydrogen peroxide (H2O2) was induced by increases in the free-electron densities on the surfaces of these AuNRs owing to oxygen plasma treatment, and Au did not dissolve under the experimental conditions. However, the potential-dependent LSPR spectra of the individual AuNRs showed similar patterns of LSPR behavior, irrespective of the duration of oxygen plasma treatment and the concentration of H2O2. Therefore, this study based on single-particle spectroelectrochemistry and cyclic voltammetry improves the understanding of the role of oxygen plasma treatment in promoting the catalytic activity of structurally stable AuNRs immobilized on an ITO surface.

Localized surface plasmon resonances of size-selected large silver nanoclusters (n = 70-100) soft-landed on a C60 organic substrate.

Silver nanoclusters (Agn NCs) exhibit a remarkable optical property known as localized surface plasmon resonance (LSPR) in the visible to ultraviolet wavelengths. In this study, we address the size gap in LSPR responses between small NCs and nano-islands by synthesizing large Agn NCs with a countable number of atoms (n = 70-100) using a magnetron sputtering method, which were precisely size-selected and soft-landed onto substrates. The monodispersed Agn NCs were immobilized on a pre-decorated substrate with fullerene (C60) molecules, and their LSPR behaviors were characterized using two-photon photoemission (2PPE) spectroscopy. Due to the distinct polarization selectivity of incident light associated with LSPR, the intensity ratio between p- and s-polarized lights (Ip/Is) in 2PPE spectroscopy serves as a reliable indicator of LSPR and its structural correlations. From n = 70 to 100, the Ip/Is value gradually decreases as the cluster size increases. This decrease is attributed to the enhancement of s-polarized light (Is), indicating that large Agn NCs on a C60 substrate undergo a deformation from spherical to flattened geometries, particularly above approximately n = 55.

Cow milk lactose inspired fabrication of zinc oxide (ZnO) nanorods for bio-applications

Nanostructured materials with different architectures and sizes are pragmatically promising candidates for biological applications. Fabrication strategy greatly controls the morphological aspects of the nanoparticles (NPs) prepared from various precursors. Here, a simple lactose inspired technique for the fabrication of zinc oxide (ZnO) nanoparticles from zinc nitrate using cow milk has been established. The synthesis was carried out at five different calcination temperatures (65, 100, 300, 500, and 700 °C). The localized surface plasmon resonance behavior of ZnO was understood from UV–Vis spectroscopy. With the increase in calcination temperature, the absorption peak maxima showed bathochromic (red) shift. Fourier transform infrared (FTIR) transmission spectra identified characteristic Zn–O absorption band in the range 480–468 cm−1. The calcined products were mainly composed of Zn and O as understood from the energy dispersive X-ray spectroscopy (EDS) analysis. The thermal behavior of the product prepared at 65 °C was studied by theromogravimetric analysis (TGA). The crystallinity of ZnO nanoparticles was analyzed by X-ray powder diffraction (XRD) technique. The crystallite size of the fabricated ZnO nanoparticles was found to be 17.5–50.25 nm depending on the calcination temperatures (300–500 °C). A rod shape morphology of ZnO nanoparticle (width: 35 nm; length: 600 nm) was observed in the scanning electron microscopy (SEM) image. ZnO nanorods (NRs) showed promising antibacterial activity against gram-positive (Bacillus cereus) and gram-negative (Pseudomonas aeruginosa) bacteria. Besides, high cytotoxic effect against Hela and BHK-21 cells was also found. This study reports a green synthesis approach for the preparation of ZnO-NRs, which is expected to find widespread biological applications leading to the advancement of nanotechnology and nanoengineering.

Fabrication of periodic Ag tetrahedral nanopyramids via H2O2-assisted nanosphere lithography for plasmonic applications

Nanosphere lithography (NSL) has been developed to prepare the monolayered hexagonally close-packed nanospheres in a large area. In our work, polystyrene (PS) sphere array was prepared by air-water interfacial floating method using hydrogen peroxide (H 2 O 2 ) solution. Compared to the conventionally used H 2 O in the air-water interfacial floating method, since the viscosity and density of 30% H 2 O 2 solution increase from 1.0 to 1.074 mPa·s and 1.0 to 1.14 g/cm 3 , respectively, the highly ordered array of PS spheres (with a density of ~1.05 g/cm 3 ) could float and self-assemble on the surface of H 2 O 2 solution without adding the surfactant or surface modification during the NSL process. Also, H 2 O 2 solution could generate the higher surface tension gradient to not only alleviate the presence of second-layer defects induced by the submerged PS nanospheres but also facilitate the self-assembly of PS sphere array due to the Marangoni convection effect. We demonstrated the effects of H 2 O 2 -assisted NSL on the second-layer defects formation, single domain size and self-assembly. In addition, the periodic Ag tetrahedral nanopyramids array (PATNA) on glass substrate was fabricated using the PS spheres array as the mask, and the optical properties of transmittance and extinction were investigated experimentally and theoretically. The PATNA prepared using the PS sphere array with H 2 O 2 assistance showed the stronger extinction and narrower FWHM compared to the one without H 2 O 2 assistance. The measured localized surface plasmon resonance peak was in good agreement with simulation results, and the PATNA with a large area on glass substrate had the potential for plasmonic applications. • Monolayer close-packed spheres are prepared by H 2 O 2 -assisted nanosphere lithography. • Second-layer defects are reduced by H 2 O 2 with higher density and viscosity than H 2 O. • Periodic Ag tetrahedral nanopyramids array on glass substrate is fabricated. • Transmittance and extinction spectra are studied experimentally and theoretically. • The nanostructure shows excellent localized surface plasmon resonance behavior.

Representation of Vivid Colors of Cyan, Magenta, Yellow, and Green in Ag Deposition-Based Plasmonic Electrochromic Device By Precise Control of Shape and Density of Deposited Ag Nanoparticles

Ag nanoparticles exhibit various colors depending on their localized surface plasmon resonance (LSPR). Based on this phenomenon, Ag deposition-based electrochromic devices can represent various optical states in a single device such as the three primary colors (cyan, magenta, and yellow), silver mirror, black and transparent.1 A control of the morphology of Ag nanoparticles can lead to dramatic changes in color, as their size and shape influence the LSPR band. For this purpose, the “voltage-step method” was applied to a Ag deposition-based EC device to obtain multiple colors by shifting the LSPR band. In this method, two different voltages are successively applied : the first voltage V 1 is applied for a very short time t 1 to initiate Ag nucleation, and the second voltage V 2 is applied for a time t 2 to promote growth of the Ag nuclei. As V 2 is more positive than the nucleation voltage, further nucleation is no longer possible during t 2. Therefore, the Ag nanoparticle growth and the resultant device color can be controlled by changing t 2.In this study2, we aimed to improve the color quality of Ag deposition-based multicolor EC devices by precisely controlling the supply of Ag+ ions to the electrode surface. Initially, the effect of coloration by decreasing the concentration of Ag+ ions in the Ag deposition-based EC device was investigated. As a result of optimizing the driving voltage, a lower concentration device (10 mM Ag+ ion) showed vivid and bright colors of cyan and magenta. This improvement was due to the generation of fine Ag nanoparticles and the prevention of the connection of Ag particles. From the electrochemical investigation, it was suggested that the slow supply rate of Ag+ ions in the lower concentration device induced electrochemical deposition of fine and isolated Ag nanoparticles.Consequently, to obtain more uniformly deposited Ag nanoparticles, the nucleation voltage of V 1 was set to a lower voltage in the 10 mM device. As a result, spherical Ag nanoparticles were successfully obtained, and the device showed yellow and green colors. By comparing the LSPR behavior of the device with that of Ag nanoparticles dispersed in solution and using FDTD calculations, the mechanism of the yellow and green colors was investigated in detail. Thus, it indicated that the yellow coloration with an absorption band in the 400–500 nm region was caused by LSPR absorption of isolated spherical Ag nanoparticles. Furthermore, it was also observed that the coexistence of isolated spherical particles and aggregations of Ag nanoparticles induced two types of LSPR bands, leading to a good green color. References A.Tsuboi, K.Nakamura and N.Kobayashi, Chem. Mater., 2014, 26, 6477-6485S.Kimura, T.Sugita, K.Nakamura and N. Kobayashi, Nanoscale, 2020 (in press)

High-Sensitive Gas-Mixture Detection Using Localized Surface Plasmon Resonance Behavior in an Optimized MDM Array

A gas-mixture sensor based on local surface plasmon resonance (LSPR) behavior in metal-dielectric-metal (MDM) periodic array is proposed. The comparisons of gas sensing performance between metal-dielectric (MD) and MDM structure are discussed for single-gas and gas-mixture separately. The influence of MDM structural parameters on the extinction spectrum and gas sensitivity are analyzed to obtain optimal parameters. By replacing the dielectric with suitable gas-sensitive films, the gas mixture of methane and hydrogen can be accurately measured without interfering with each other. The methane and hydrogen sensitivities can reach to −3.435nm /% and −0.72nm /%, respectively. The results also verify the feasibility of multi-channel gas detection and provide an effective method for gas component analysis.

Fluorometric virus detection platform using quantum dots-gold nanocomposites optimizing the linker length variation

In this study, a tunable biosensor using the localized surface plasmon resonance (LSPR), controlling the distance between fluorescent CdZnSeS/ZnSeS quantum dots (QDs) and gold nanoparticles (AuNPs) has been developed for the detection of virus. The distance between the AuNPs and QDs has been controlled by a linkage with a peptide chain of 18 amino acids. In the optimized condition, the fluorescent properties of the QDs have been enhanced due to the surface plasmon effect of the adjacent AuNPs. Successive virus binding on the peptide chain induces steric hindrance on the LSPR behavior and the fluorescence of QDs has been quenched. After analyzing all the possible aspect of the CdZnSeS/ZnSeS QD-peptide-AuNP nanocomposites, we have detected different concentration of influenza virus in a linear range of 10−14 to 10−9 g mL−1 with detection limit of 17.02 fg mL−1. On the basis of the obtained results, this proposed biosensor can be a good alternative for the detection of infectious viruses in the various range of sensing application.

Effects of surface ligands on localized surface plasmon resonance and stabilization of Cu2−xSe nanocrystals

Cubic Cu2−xSe nanocrystals (NCs) exhibit a strong localized surface plasmon resonance (LSPR) absorption in the near-infrared (NIR) region, in which the LSPR wavelength and stability are significant for the NIR-region applications in photo-thermal therapy and photoacoustic imaging. Herein, we have systematically studied the effects of surface ligands with varying the feeding ratio of oleylamine (OM) to oleic acid (OA) on LSPR behavior and stabilization of Cu2−xSe NCs, which were synthesized by using a typical hot-injection method. The LSPR wavelength of the as-obtained Cu2−xSe NCs could be tuned from 1260 to 1030 nm with an increase of the feeding ratio of OM to OA. Furthermore, these Cu2−xSe NCs showed different LSPR stability with varying feeding ratios of OM to OA. For the Cu2−xSe NCs synthesized in the presence of only OM, the LSPR could keep stable basically after exposure to air for 60 days. However, in the feeding ratio of OM to OA of 7:3 and 5:5 cases, the LSPR extinction spectra showed an obvious blue-shift in the wavelength. The characterized results indicated the different surface ligands had significant effects on the LSPR behavior and stabilization, and the LSPR change was in good agreement with the calculated results based on the Mie-Drude model. This work provides a new research idea for tuning the LSPR behavior of copper chalcogenide NCs.

Dominant role of iron oxides in magnetic circular dichroism of plasmonic-magnetic Au-Fe3−xO4 heterodimer nanostructures

Plasmon-tuned magneto-optical (MO) properties enable design concepts of MO devices with various nanoarchitectures. In this study, magnetic circular dichroism (MCD) is presented in plasmonic-magnetic Au-Fe3−xO4 heterodimer nanostructures dispersed in solution. The heterodimers are synthesized by thermal decomposition of Fe(III) precursors in the presence of preformed Au nanoparticles. The extinction spectrum exhibits a localized surface plasmon resonance (LSPR) peak, which is red-shifted with respect to the isolated Au particle resonance. On the other hand, the MCD response is overwhelmingly dominated by iron oxide counterparts consisting of multiphase magnetite (Fe3O4)/maghemite (γ-Fe2O3). No appreciable LSPR-enhancement in the MO response is found. As for the effect of the magnetic component on the LSPR behavior of Au, a decrease in the magnetoplasmonic response is observed. This suggests a reduction of the effective magnetic field to the Au counterparts, which can probably be due to magnetic shielding by the iron oxides in the near vicinity of Au nanoparticles.

A High-Sensitivity Methane Sensor with Localized Surface Plasmon Resonance Behavior in an Improved Hexagonal Gold Nanoring Array.

This paper proposes a methane sensor based on localized surface plasmon resonance (LSPR) of a hexagonal periodic gold nanoring array. The effects of structural parameters on the extinction spectrum and refractive index (RI) sensitivity are analyzed to obtain optimal parameters. In particular, the RI sensitivity can reach 550.08 nm/RIU through improvement of the sensor structure, which is an increase of 17.4% over the original value. After coating a methane-sensitive membrane on the inner and outer surfaces of the gold rings, the methane concentration can be accurately measured with a gas sensitivity of −1.02 nm/%. The proposed method is also applicable to quantitative analyses of components concentration and qualitative analyses of gas composition.

Wulff-Based Approach to Modeling the Plasmonic Response of Single Crystal, Twinned, and Core-Shell Nanoparticles.

The growing interest in plasmonic nanoparticles and their increasingly diverse applications is fuelled by the ability to tune properties via shape control, promoting intense experimental and theoretical research. Such shapes are dominated by geometries that can be described by the kinetic Wulff construction such as octahedra, thin triangular platelets, bipyramids, and decahedra, to name a few. Shape is critical in dictating the optical properties of these nanoparticles, in particular their localized surface plasmon resonance behavior, which can be modeled numerically. One challenge of the various available computational techniques is the representation of the nanoparticle shape. Specifically, in the discrete dipole approximation, a particle is represented by discretizing space via an array of uniformly distributed points-dipoles; this can be difficult to construct for complex shapes including those with multiple crystallographic facets, twins, and core–shell particles. Here, we describe a standalone user-friendly graphical user interface (GUI) that uses both kinetic and thermodynamic Wulff constructions to generate a dipole array for complex shapes, as well as the necessary input files for DDSCAT-based numerical approaches. Examples of the use of this GUI are described through three case studies spanning different shapes, compositions, and shell thicknesses. Key advances offered by this approach, in addition to simplicity, are the ability to create crystallographically correct structures and the addition of a conformal shell on complex shapes.

Zigzag Localized Surface Plasmon Resonance Wavelength Shift of Asymmetric V-Shape Ag Nanorods

Asymmetry could significantly affect a nanoparticle’s localized surface plasmon resonance (LSPR) behaviors, although limited attention has been drawn on this fascinating phenomenon. In this work, asymmetry’s influence on the LSPR behaviors of V-shape Ag nanorods was systematically studied. The introduction of asymmetry generated a zigzag resonance wavelength shift pattern with alternative blue and red shifts. In the zigzag patterns, the number of bends proportionally increased with the order of resonance mode: from the first to the fifth mode, the patterns showed 0 to 4 bends, respectively. Moreover, wavelength extremums were always reached at certain asymmetry degrees of k/n, where n is the resonance order number and k is any integer from 1 to n – 1. Detailed explanations contributing to these phenomena were discussed at last, which might relate to the variation of pole distance and the corresponding energy fluctuation as the asymmetry degree changed.

Engineering a plasmonic sensing platform for Candida albicans antigen identification

We established a procedure to develop a localized surface plasmon resonance (LSPR) optical sensor platform for immunoassay. Computational simulations, focused on the assessment of the LSPR spectrum and spatial distribution of the electromagnetic field enhancement near the metallic nanoparticle, were used to engineer a nanostructured-sensing platform. Crucial parameters that rule the LSPR sensor performance, as bulk and molecular sensitivity, were evaluated, guiding the development of the optical platform. An LSPR surface-based platform composed of silver nanospheres adhered on a glass slide and functionalized with monoclonal anti-Candida antibodies of the IgG class was fabricated. Molecular biosensing was demonstrated by the identification of Candida albicans antigen. In particular, C. albicans is the most common species involved in a variety of hospital yeast infections. The developed sensing platform was able to identify C. albicans antigen concentration as low as 50 ng / mL, indicating the viability of exploring LSPR effect on C. albicans antigen biosensor. Moreover, this work provides insight on the LSPR behavior due to the adsorption of molecules layer on a nanoparticle surface, establishing a paradigm on engineering LSPR biosensor.

Coupling of a light-emitting diode with surface plasmon polariton or localized surface plasmon induced on surface silver gratings of different geometries.

A metal grating on top of a light-emitting diode (LED) with a designed grating period for compensating the momentum mismatch can enhance the surface plasmon polariton (SPP) coupling effect with the quantum wells (QWs) to improve LED performance. Here, we demonstrate the experimental results showing that the induced localized surface plasmon (LSP) resonance on such a metal grating can dominate the QW coupling effect for improving LED performance, particularly when grating ridge height is large. The finding is illustrated by fabricating Ag gratings on single-QW, green-emitting LEDs of different p-type thicknesses with varied grating ridge height and width such that the distance between the grating ridge tip and the QW can be controlled. Reflection spectra of the Ag grating structures are measured and simulated to identify the SPP or LSP resonance behaviors at the QW emission wavelength. The measured results of LED performances show that in the LED samples under study, both SPP and LSP couplings can lead to significant enhancements of internal quantum efficiency and electroluminescence intensity. At the designated QW emission wavelength, with a grating period theoretically designed for momentum matching, the LSP coupling effect is stronger, when compared with SPP coupling.

Engineering a Localized Surface Plasmon Resonance Platform for Molecular Biosensing

In this work, we introduce a new perspective on the development of Localized Surface Plasmon Resonance (LSPR) optical biosensors. Computational simulations, focused on the assessment of the LSPR spectrum and spatial distribution of the electromagnetic field enhancement near a metallic nanoparticle, elucidated the behavior of crucial parameters, as figure of merit, bulk and molecular sensitivity, which governs a LSPR sensor performance. Gold and silver nanospheres were explored as starting point to assess plasmonic optical characteristics of the nanostructured sensor platform. Here, for the first time in the literature, Campbell’s model was evaluated exploiting a NP size-dependence approach. The theoretical analyses indicate a nonlinear behavior of the bulk and molecular sensitivity as function of the NP size. Substantial LSPR peak shifts due to the adsorption of molecules layer on a NP surface were observed for nanoparticles with ~5 nm and ~40 nm radius. Moreover, on molecular sensing, LSPR peak shift is also determined by the thickness of adsorbed molecular shell layers. We observed that for 40 nm radius gold and silver nanospheres, significant LSPR peak shift could be induced by small (few nm) thickness change of the adsorbate shell layer. Moreover, this work provides insights on the LSPR behavior due to adsorption of molecular layer on a NP surface, establishing a new paradigm on engineering LSPR biosensor. Furthermore, the proposed approach can be extended to engineer an efficiently use of different nanostructures on molecular sensing.

Aggregation-Driven Controllable Plasmonic Transition of Silica-Coated Gold Nanoparticles with Temperature-Dependent Polymer-Nanoparticle Interactions for Potential Applications in Optoelectronic Devices.

Localized surface plasmon resonance (LSPR) effect relies on the shape, size, and dispersion state of metal nanoparticles and can potentially be employed in many applications such as chemical/biological sensor, optoelectronics, and photocatalyst. While complicated synthetic approaches changing shape and size of nanoparticles can control the intrinsic LSPR effect, here we show that controlling interparticle interactions with silica-coated gold nanoparticles (Au@SiO2 NPs) is a powerful approach, permitting wide range of optical bandwidth of gold nanoparticles with great stability. The interparticle interactions of Au@SiO2 NPs are controlled through concentration-, temperature-, and time-dependent polymer-induced interactions. The polymer-induced interactions modulate the state of particle dispersion, resulting an effective plasmonic shift by more than 200 nm. We further explore the microstructure of particle aggregation and explain mechanisms of plasmonic shift based on the results of small-angle X-ray scattering (SAXS) and discrete dipole approximation (DDA) calculation. We show that an effective control of LSPR behavior is now available through trapped aggregation of Au@SiO2 NPs with temperature variation. We anticipate that the suggested strategy can be employed in many practical applications such as optical bioimaging and optoelectronic devices.

Surface plasmon lithography beyond the diffraction limit

Due to the light’s diffraction feature, conventional optical lithography methods have been suffering from the diffraction limit of resolution, which imposes great obstacles for obtaining nano patterns with ultra-violet and deep ultra-violet light source. Surface plasmons (SPs) are the free electron density waves confined at the interface of metal and dielectric medium, which exhibits unique sub-diffraction optical characteristic in SP propagation, focusing and imaging performances. In recent years, benefiting from SPs’ features beyond the diffraction limit, researchers have proposed a variety of SP lithography methods in the manner of interference, imaging and direct writing, demonstrating both in theoretical simulations and experiments that the sub-diffraction resolution could be readily obtained in SP lithography just using ultra-violet light source and single exposure process. The SPs interference lithography is simple and easy to realize nano periodic patterns with short wavelength of SPs, but usually deliver some shortcomings, like greatly restricted interference area size and complex fabrications of exciting structures. Bulk plasmon polaritons formed by greatly coupled SPs was proposed and demonstrated in our work for deep subwavelength large area interference lithography without the necessity of subwavelength exciting structures. SPs lithography in direct writing manner mainly originates from localized surface plasmon resonance behaviors of nano particles or metallic tips, further investigations of bow-tie structure and SP focusing lens with specific nano structures deliver enhanced resolution and intensity efficiency and help to realize point to point writing lithography with much more flexibility. Plasmonic lens imaging lithography seems to be particular interesting for applications as projecting nano irregular patterns in one exposure step. Superlens, as a simplified version of perfect lens, provides the physical prototype of SP imaging lithography. Further, the contributions of metal-dielectric-metal cavity lens and SP wave front engineering methods, like off axis illumination and near field proximity corrections, deliver great quality improvement of lithography patterns, including resolution, aspect ratio and fidelity. Half pitch resolution down to 22 nm (~1/17 light wavelength) has been obtained in SP imaging lithography experiments. Also some functional devices, like meta-lens and polarizer, have been successfully fabricated by plasmonic lens imaging lithography. It shows that SP helps to give a potentially promising access for high resolution, efficient, large area and low cost nano lithography tools. Besides the review and analysis of research progress, representative achievements of SP lithography, the remained problems and outlook of further developments are presented as well in this review.

Rational design of Ag@Ag-Bi-KBa2Ta5O15 nanocomposites as efficient plasmonic photocatalysts for degradation of organic pollutants in water under visible light

Bismuth (Bi) and silver (Ag) co-doped KBa2Ta5O15 nanocomposites were fabricated and modified with Ag nanoparticles (NPs) to form a novel visible light-driven plasmonic photocatalyst (Ag@Ag-Bi-KBT) for photodegradation applications. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectroscopy and high resolution transmission electron microscopy have been conducted to investigate the structural, morphological, electronic and optical characteristics of the photocatalysts. The photocatalytic activity of the Ag@Ag-Bi-KBT nanocomposites has been systematically evaluated by photodegradation of four organic contaminants (rhodamine B, orange G, methyl orange and bisphenol A) in aqueous solution under visible light irradiation (λ>420nm). The degradation mechanism over Ag@Ag-Bi-KBT is discussed. Ag@Ag-Bi-KBT exhibits high photocatalytic activity under visible light irradiation, mainly due to increased reaction sites and strong visible light absorption by Bi- and Ag-co-doping, as well as to the optimized localized surface plasmon resonance behavior and efficient charge separation resulting from Ag NPs.

Polarization Anisotropy of Multiple Localized Plasmon Resonance Modes in Noble Metal Nanocrescents

Multiple localized surface plasmon resonance (LSPR) modes induced in gold and silver nanocrescents exhibit anisotropic behavior with respect to polarization of incident light. Extinction spectroscopy with polarization control was used to characterize the optical properties of asymmetric nanocrescents with diameters ranging from 100 to 500 nm. The analysis shows that selective induction of distinct dipole and quadrupole LSPR modes can be accomplished through polarization of incident light. Finite-difference time-domain calculations of the LSPR responses of the nanocrescent corroborate the polarization-dependent optical behavior. Simulations reveal optical near field enhancements with unique spatial patterns associated with the individual resonance modes depending on the polarization and wavelength of incident light. Quantitative analysis of the anisotropic LSPR behavior supports the potential for controlling the near field through selective induction of specific resonance modes with particular near field d...