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Localized surface plasmon interaction of colloidal gold nanoparticles and the resultant changes in the linewidth of plasmon bands are reported. The evolution of the plasmon band in colloids is investigated by increasing the number of particles per unit volume. The volume of the solvent is reduced from 15 to 3 ml by the simple evaporation method. It is observed that the linewidth of the plasmon band varies in a non-uniform manner, which is attributed to the interaction of plasmons from the surface of gold nanoparticles rather than aggregation effects. Indication of aggregation effects such as a progressive redshift in plasmon peak and continuous broadening of linewidth were absent. Gold nanoparticles are prepared using laser ablation of the gold target with nanosecond laser pulses using pure water as a solvent. Change in the linewidth of plasmon bands on colloidal gold nanoparticles with minimized size distribution prepared using laser fluences viz. 5.09, 10.19, 15.28, 20.38 and 25.48 J/cm2 are explored.

Metasurfaces and terahertz spectrum are promising parts of future communication, ecosystems. Nevertheless, studies have shown that reported metasurfaces in this part of, the spectrum are not sufficiently efficient. In this research, three different applications, at the THz spectrum which are based on metasurface structures are studied as the main, topics of research. First, a novel terahertz (THz) spectroscopy system is proposed which, is based on a graphene-based metasurface. The proposed sensor operates in reflection, mode over a broad range of frequency bands (0.2 − 6 THz) and can detect relative, permittivity of up to 4 with a resolution of 0.1 and a thickness ranging from 5 μm to, 600 μm with a resolution of 0.5μm. The proposed spectroscopy technique utilizes some, unique spectral features of a broadband reflection wave including Accumulated Spectral, power (ASP) and Averaged Group Delay (AGD), which are independent of resonance, frequencies and can operate over a broad range of the spectrum. Following this, an, efficient terahertz (THz) photoconductive antenna (PCA) are proposed. The antenna, is designed for THz continuous wave (CW) applications in the frequency range of 0.5-3, THz. Owing to plasmonic excitation, the optical-to-electrical efficiency of photomixer, is increased by a factor of 100 while there is a 4-fold reduction in size compared to those, with similar radiation features. Finally, a novel metasurface design is proposed for the, first time ever which has addressed some fundamental challenges in metasurface design, and has introduced dense metasurface for the first time. In this chapter, an algorithm, is proposed for the design of metasurface which exploited Delta-Sigma concept from, temporal domain to spatial domain to increase the spatial sampling of the incident, wave in reflecting/transmission metasurfaces. In this algorithm, the design procedure, considers real-world response of the structure instead of conventional analysis of meta, surfaces. The proposed algorithm brings about to achieve very efficient beam-forming of, reflecting/transmission metasurface. It is shown that the proposed technique improved, the efficiency of metasurface design significantly and can enhance the control over the, metasurface design unprecedentedly.

Z-scheme heterojunctions are fundamentally promising yet practically appealing for photocatalytic hydrogen (H2) production owing to the enhanced redox power, spatial separation of charge carriers, and broad-spectrum solar light harvesting. The charge-transfer dynamics at Z-scheme heterojunctions can be accelerated by inserting charge-transfer mediators at the heterojunction interfaces. In this study, we introduce Au nanoparticle mediators in the Z-scheme W18O49/g-C3N4 heterostructure, which enables an improved H2 production rate of 3465 μmol/g·h compared with the direct Z-scheme W18O49/g-C3N4 (1785 μmol/g·h) under 1 sun irradiation. The apparent quantum yields of H2 production with W18O49/Au/g-C3N4 are 3.9% and 9.3% at 420 and 1200 nm, respectively. The improved photocatalytic H2 production activity of W18O49/Au/g-C3N4 is attributable to the triple-channel charge-transfer mechanism: channel I─Z-scheme charge transfer facilitates charge separation and increased redox power of the photoexcited electrons; channels II and III─the localized surface plasmon resonances from Au (channel II) and W18O49 (channel III) enable light harvesting extension from visible to near-infrared wavelengths.

Tunable extraordinary optical transmission (EOT) with graphene is realized using a novel metallic ring–rod nested structure in the terahertz frequency regime. The generated double-enhanced transmission peaks primarily originate from the excitation of localized surface plasmon resonances (LSPRs). On using graphene, the resonating surface plasmon distribution changes in the reaction plane, which disturbs the generation of LSPRs. By regulating the Fermi energy (Ef) of the graphene to reach a certain level, an adjustment from bimodal EOT to unimodal EOT is obtained. As the Ef of the graphene integrated beneath the rod increases to 0.5 eV, the transmittance of the peak at 2.42 THz decreases to 6%. Moreover, the transmission peak at 1.77 THz virtually disappears due to the Ef increasing to 0.7 eV when the graphene is placed beneath the ring. The significant tuning capabilities of the bimodal EOT indicate its promising application prospects in frequency-selective surfaces, communication, filtering, and radar.

Two-dimensional transition metal dichalcogenide (TMDC) nanocrystals (NCs) exhibit unique optical and electrocatalytic properties. However, the growth of uniform and high-quality NCs of monolayer TMDC remains a challenge. Until now, most of them are synthesized via a solution-based hydrothermal process or ultrasonic exfoliation method, in which the capping ligands introduced from organic solution often quench the optical and electrocatalytic properties of TMDC NCs. Moreover, it is difficult to homogeneously disperse the solution-based TMDC NCs on a substrate for device fabrication, since the dispersed NCs can easily aggregate. Here, we put forward a novel CVD method to grow closely spaced MoS2 NCs around 5 nm in lateral size. TEM and AFM characterizations demonstrate the monolayer and high-crystalline nature of MoS2 NCs. An obvious blue-shift with 130 meV in photoluminescence signals can be observed. The MoS2 NCs also show an outstanding surface-enhanced Raman scattering for organic molecules due to their localized surface plasmon and abundant edge sites and exhibit excellent electrocatalytic properties for the hydrogen-evolution reaction with a very low onset potential of ∼50 mV and Tafel slope of ∼57 mV/decade. Finally, we further demonstrate this kind of CVD method as a versatile platform for the growth of other TMDC NCs, such as WSe2 and MoSe2 NCs.

The performance improvement of solid-state triplet-triplet annihilation-based photon upconversion (TTA-UC) systems is required for the application to various solar devices. The performance can be improved by making use of the local strong electric field generated through the excitation of localized surface plasmon (LSP) resonance of metal nanostructures. However, since the improvement is effective only within the limited nanospace around nanoparticles (i.e., the near-field effect), a methodology for improving the performance over a wider spatial region is desirable. In this study, a significant improvement in the threshold light excitation intensity (Ith) (77% decrease) as the figure of merit and the upconverted emission intensity (6.3 times enhancement) in a solid-state TTA-UC film with a thickness of 3 μm was achieved by stacking the film with periodic Ag half-shell arrays. The highest-enhanced upconverted emission was obtained by tuning the diffuse reflectance peak, which results from the excitation of LSP resonance of the Ag half-shell arrays, to overlap well with the photoexcitation peak of the sensitizer in the TTA-UC film. The intensity of the enhanced upconverted emission was independent of the distance between the lower edge of the TTA-UC film and the surface of half-shell arrays in the nanometer order. These results suggest that the performance improvement was attributed to the photoexcitation enhancement of the sensitizer by elongating the excitation light path length inside the TTA-UC film, which was achieved through a strong backward scattering of the incident light based on the LSP resonance excitation (i.e., the far-field effect). In addition, the upconverted emission was improved using half-shell arrays comprising low-cost Al, although the enhancement factor was 3.5, which was lower than that of Ag half-shell arrays. The lower enhancement may be attributed to a decrease in the backward scattering of the excitation light owing to the intrinsic strong interband transition of Al at long visible wavelengths.

Ag loaded Ga2O3 photocatalysts are well known to be highly active for the CO2 reduction with water to CO. However, Ag changes its chemical state during the reaction, resulting in the decrease of its photocatalytic activity. To examine the chemical state change during the photocatalytic CO2 reduction, we have attempted a real time observation of the change in the chemical and physical states of Ag co-catalyst loaded on Ga2O3 by monitoring UV–vis reflectance spectra under the atmosphere simulating the photocatalytic CO2 reduction. In UV–vis spectra, two characteristic absorptions appeared at around 450 nm and 600 nm corresponding to resonance absorptions of localized surface plasmon (LSPR) of Ag nanoparticles (Ag-NPs) and Ag in metallic state. The LSPR absorption appeared as light irradiation started and grew with the time. It was revealed that Ag on Ga2O3 was initially in the oxidized state and reduced by the light irradiation to be Ag-NPs. Further light irradiation enlarged the size of Ag-NPs to be the metallic state especially under atmosphere with water. Under CO2 atmosphere, Ag-NPs remained small after further light irradiation. These results suggest that Ag initially loaded on Ga2O3 in the oxidized state was reduced to be dissolved as Ag+ in water and precipitated as Ag-NPs. Then, some of Ag-NPs aggregated to be larger Ag particles or in the metallic state. Such reduction process depends on gas species of the system, i.e. water promoted the formation of Ag-NPs while CO2 suppressed the formation Ag-NPs.

Degenerately doped metal-oxide nanocrystals (NCs) show localized surface plasmon resonances (LSPRs) that are tunable via their tunable excess charge-carrier densities. Modulation of excess charge carriers has also been used to control magnetism in colloidal doped metal-oxide NCs. The addition of excess delocalized conduction-band (CB) electrons can be achieved through aliovalent doping or by postsynthetic techniques such as electrochemistry or photodoping. Here, we examine the influence of charge-compensating aliovalent dopants on the potentials of excess CB electrons in free-standing colloidal degenerately doped oxide NCs, both experimentally and through modeling. Taking Sn4+:In2O3 (ITO) NCs as a model system, we use spectroelectrochemical techniques to examine differences between aliovalent doping and photodoping. We demonstrate that whereas photodoping introduces excess CB electrons by raising the Fermi level relative to the CB edge, aliovalent impurity substitution introduces excess CB electrons by stabilizing the CB edge relative to an externally defined Fermi level. Significant differences are thus observed electrochemically between spectroscopically similar delocalized CB electrons compensated by aliovalent dopants and those compensated by surface cations (e.g., protons) during photodoping. Theoretical modeling illustrates the very different potentials that arise from charge compensation via aliovalent substitution and surface charge compensation. Spectroelectrochemical titrations allow the ITO NC band-edge stabilization as a function of Sn4+ doping to be quantified. Extremely large capacitances are observed in both In2O3 and ITO NCs, making these NCs attractive for reversible charge-storage applications.

The optical and dielectric properties of plasmonic of Fe2O3/Au and Fe3O4/Au core/shell nanoparticles were studied using Finite Element computational approach. The optical response of these nanostructures was investigated through the computation of the real and the imaginary parts of the effective dielectric permittivity and the absorption cross-section in the visible-near infrared spectral range. Our findings are as follows. Firstly, we have compared our obtained numerical results with those predicted by Maxwell–Garnett effective medium theory. Secondly, the obtained results reveal that the localized surface plasmons resonance (LSPR) peak shifts to near infrared for a Fe2O3/Au-nanoparticle are similar to that of a Fe3O4/Au-nanoparticle having the same geometric parameters. Thirdly, the optical characteristics of the plasmonic nanoparticles were also studied. Finally, we hope that the developed numerical method can be extended to investigate the electromagnetic coupling within or between particles and its effect on the plasmonic behaviors. This makes the core/shell composite nanoparticles extremely interesting for magnetic, optical and biomedical applications.

Recently, localized surface plasmon resonances (SPRs) of metallic nanoparticles (NPs) have been widely used to construct plasmonic nanohybrids for heterogeneous photocatalysis. For example, the combination of plasmonic Au NPs and TiO2 provides pure TiO2 visible-light activity. The SPR effect induces an electric field and consequently enhances light scattering and absorption, favoring the transfer of photon energy to hot carriers for catalytic reactions. Numerous approaches have been dedicated to the improvement of SPR absorption in photocatalysts. Here, we have designed a core@shell-satellite nanohybrid catalyst whereby an Ag NP core, as a plasmonic resonator featuring unique dual functions of strong scattering and near-field enhancement, is encapsulated by SiO2 and TiO2 layers in sequence, with Au NPs on the outer surface, Ag@SiO2@TiO2-Au, for efficient plasmonic photocatalysis. By varying the size and number of Ag NP cores, the Au SPR can be tailored over the visible and near-infrared spectral region to reabsorb the scattered photons. In the presence of the Ag core, the incident light is efficiently confined in the reaction suspension by undergoing multiple scattering, thus leading to an increase of the optical path to the photocatalysis. Moreover, using numerical analysis and experimental verifications, we demonstrate that the Ag core also induces a strong near-field enhancement at the Au-TiO2 interface via SPR coupling with Au. Consequently, the activity of the TiO2-Au plasmonic photocatalyst is significantly enhanced, resulting in a high H2 production rate under visible light. Thus, the design of a single structural unit with strong scattering and field enhancement, induced by a plasmonic resonator, is a highly effective strategy to boost photocatalytic activity.

The extension of plasmonics to materials beyond the conventional noble metals opens up a novel and exciting regime after the inspiring discovery of characteristic localized surface plasmon resonances (LSPRs) in doped semiconductor nanocrystals originating from the collective oscillations of free holes in the valence band. We herein prepare colloidal monodisperse eccentric dual plasmonic noble metal-nonstoichiometric copper chalcogenide (Au@Cu2−xSe) hybrid hetero-nanostructures with precisely controlled semiconductor shell size and two tunable LSPRs in both visible (VIS) and near-infrared (NIR) regions associated with Au and Cu2−xSe, respectively. Through systematic evaluations of the photocatalytic performance of Au@Cu2−xSe upon sole NIR and dual VIS + NIR simultaneous excitations, we are capable of unambiguously elucidating the role of plasmonic coupling between two dissimilar building blocks on the accelerated photocatalytic reactions with greater rate constants from both experimental and computational perspectives. The significantly enhanced strength of the electromagnetic field arising from efficient plasmonic coupling under the excitation of two LSPRs results in the superior activities of dual plasmonic Au@Cu2−xSe in photocatalysis. The new physical and chemical insights gained from this work provide the keystone for the rational design and construction of high-quality dual- or even multi-plasmonic nano-systems with optimized properties for widespread applications ranging from photocatalysis to molecular spectroscopies.

Infrared phototransistors with very high performance show great potential in optoelectronic application, attributable to the intrinsic high transconductive gain of the transistor structure and therefore very large photo-responsivity. To distinguish multispectral information with phototransistors, however, the coincident spectral light has to been laterally dispersed and thereby coupled to the individual photo-gates sensing different target bands. Here, the dual-frequency plasmonic photo-coupler based on a single perforated metallic layer is numerically designed in the infrared region to improve photon absorption efficiency at two target wavelengths. The geometric parameters of the plasmonic grating composed of large and small cross-shaped holes are independently tuned to control the resonance frequencies under different incident (x- and y-) polarization conditions. While the dual-frequency resonant modes are induced by the hybridization between localized surface plasmons (LSPs) and propagating surface plasmons (PSPs), it is found that LSPs play the dominant role and can be effectively adjusted to achieve the target dual-frequency response. More importantly, the spectral response with low- (high-) frequency resonance corresponding to large (small) cross-hole region matches the spatially distributed photogates of the phototransistor structure and therefore realizes near-field enhancement and hence large photoresponsivity at target dual frequencies. In addition, the spectral response for x- and y-polarizations can be unified despite of the apparently broken symmetry between these two polarizations. Our work provides a general strategy to realize sensitive multiband-infrared phototransistors which require only state-of-the-art planar technology and are applicable for highly sensitive infrared photodetection.

In this research, a theoretical and experimental study of bimetallic gold and platinum nanoparticles is reported. From the green synthesis approach, a combination of rongalite with sucrose is used as a reducing and stabilizing agent. Nanoalloys (Au@Pt) and Pt-core/Au-shell nanoparticles were obtained according to the synthesis process used, and the optical response was analyzed. For nanoalloys, two absorption bands were associated with localized surface plasmon resonances. These were located at 300 nm and another between 350 nm and 365 nm, respectively. For core/shell type nanoparticles, an absorption band centered at 530 nm was observed. The images obtained by transmission electronic microscopy (TEM) confirmed the presence of quasi-spherical nanoparticles with core/shell type configurations. Numerical calculations of the cross sections for a Pt-core/Au-shell nanoparticle with spherical geometry was used to establish a comparison with the experimental absorption in the ultraviolet-visible (UV–Vis) spectrum. Complementary, the TEM images and chemical analysis by energy dispersive spectroscopy (EDS) showed the presence of core/shell type nanoparticles.

CuS materials exhibit excellent near infrared (NIR) photoabsorption and photothermal effect, but they are lack of magnetic resonance imaging (MRI) ability. Fe-based nanomaterials possess MRI capacity, but they usually exhibit poor NIR photoabsorption. In order to solve the above problems, we synthesize three kinds of CuxFeySz samples, including FeS2, CuFeS2 and Cu5FeS4 nanomaterials. With the Cu/Fe ratios increase from 0/1.0 to 1.0/1.0 and 5.0/1.0, the localized surface plasmon resonances (LSPRs) characteristic peaks shift to longer wavelength, and the photothermal transduction efficiencies go up from 24.4% to 36.6% and 45.9%. Thus, Cu5FeS4 is found to be the most excellent sample. Especially, Cu5FeS4 exhibits photothermal-enhanced Fenton effect, which can produce hydroxyl radical (·OH) under a wide pH range (e.g., pH = 5.4–7.4) to realize the chemodynamic effect. In addition, Cu5FeS4 can be employed as an efficient MRI contrast agent. When Cu5FeS4 dispersion is intravenously injected into the mouse, the tumor can be detected by MRI as well as thermal imaging, and eliminated through photothermal-enhanced chemodynamic effect. Therefore, Cu5FeS4 can be used as an efficient “one-for-all” type agent for MRI-guided photothermal-enhanced chemodynamic therapy of tumor.

Plasmonic composites consisting of silver nanostructures and zinc oxide semiconductor have better photocatalytic performance than pure zinc oxide. To prepare the composites, nanostructures of zinc oxide particles, gold spheres, and three different silver morphology including cubes, spheres, and wires were synthesized. A detailed study of the main mechanisms governing the activity of plasmonic photocatalysts showed that the improvement of photocatalytic performance is attributed to localized surface plasmon resonance-mediated energy transfer from silver to zinc oxide. This mechanism, which is performed using non-radiative (near-field) and radiation (far-field) processes, led to an increase in the concentration of e−/h+ pairs near the semiconductor. We also showed that the increase of the photocatalytic activity depends on the shape of the silver nanostructures in the composites. Our theoretical and experimental studies have shown that composites containing silver cubes have the highest increase of photocatalytic activity compared to other morphologies. The percentage of photocatalytic degradation of methylene blue solution in presence of silver cubes was about 15% higher than that of other morphologies. Therefore, by controlling the shape of noble metal nanostructures, the photocatalytic activity of a semiconductor can be maximized and adjusted.

Thin films with tunable optical properties from yellow to metallic were prepared from a monolayer coating of silver nanoparticles (AgNP) onto a polyelectrolyte multilayer (PEM) thin film. The AgNP were synthesized using various concentrations of stabilizing polyelectrolytes leading to a competitive adsorption concept in which AgNP compete with excess polyelectrolytes to coat the cationic PEM top layer. The AgNP were synthesized by chemical reduction of Ag salts using poly(styrene 4-sulfonic acid-co-maleic acid) (PSS-co-MA) as stabilizing agent to produce nanoparticles coated with both a strong acid (sulfonic) and a weak acid (carboxylic) moiety. Although all the nanoparticle solutions displayed a characteristic bright yellow due to the localized surface plasmon band around 420 nm, the monolayer films of nanoparticles obtained after dipping displayed striking different optical properties. When using a high PSS-co-MA content in the solution, a pale-yellow film was obtained which color shifted to orange and metallic when the capping concentration was decreased from 0.25 to 0.001 mM. The optical properties of the AgNP film could be further changed by galvanic replacement of the Ag with gold ions to produce a gold monolayer. These results are interesting to produce surface with tunable catalytic properties, tunable optical properties, or to be used as primer for the metallization of polymeric surfaces.

Silver nanoparticles (Ag NPs) coated by an aqueous emulsion of copolymer were elaborated in a short time using polyol process and microwave (MW) heating. This approach is based on reducing AgNO3 powder in the presence of two main components; ethylene glycol as a dispersed medium and an industrial copolymer (latex) as protecting agent. The structural, morphological and optical properties of the prepared silver nanoparticles have been investigated by UV–Vis spectroscopy, Infrared Spectroscopy (IR), X Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). It was found that all these properties are strongly correlated to the latex copolymer concentration and the MW heating process. The absorption band was determined by UV Visible spectra, showing several bands (localized surface Plasmon band) in the visible region at wavelengths between 410 and 430 nm. The TEM analysis of the obtained products indicates the presence of straight nanowires and dispersed, spherical silver nanoparticles with well-controlled size ranging from 7 to 20 nm. The X Ray Diffraction showed that silver nanoparticles synthesized exhibit face centered cubic (fcc) structure. The infrared spectra show the strong coordination between the surface of silver particles and molecules of latex by O–H and C=O groups. Antimicrobial activity of latex/Ag NPs against E. coli, Staphylococcus aureus, and Pseudomonas aeruginosa has been also demonstrated. The results indicated that latex/AgNPs may damage the structure of bacterial cell membrane.

Developing a simple structure using low-cost material that enables both large-scale fabrication and broadband absorption response is highly desirable but very challenging for achieving high-performance metamaterial absorber. Herein, we propose and numerically investigate an ultra-broadband and wide-angle insensitive perfect metamaterial absorber in the ultraviolet to near-infrared (UV–NIR) region based on a simple metal–dielectric–metal structure. The proposed absorber structure consists of a periodic array of a tungsten hexagonal prism and a tungsten ground plane separated by a silicon dioxide dielectric substrate. The proposed absorber achieves an ultra-broadband absorption response in the range of 275–1000 nm with an absorptivity above 90 $$\%$$ and a relative bandwidth of 106.8 $$\%$$ at normal incidence, which covers from the UV to NIR region. The absorption efficiency is maintained with the figure of merit $$\eta _{OBW}$$ higher than 90 $$\%$$ for a wide incident angle up to 40 $$^{o}$$ for transverse electric (TE) polarization and 65 $$^{o}$$ for transverse magnetic (TM) polarization. The effects of structural parameters and different metallic materials on the absorption performance are presented. In addition, the physical mechanism is analyzed using the surface density and distributions of electric and magnetic fields that are attributed to both localized surface plasmon (LSP) and propagating surface plasmon (PSP) resonances. Owing to outstanding merits of simple structure, low cost, and high absorption performance, the designed absorber can be suitable for many applications in the UV–NIR spectrum such as thermal emitters and solar cells.

In plasmonic catalysis, localized surface plasmons can be leveraged to drive chemical reactions. This approach is promising for catalyzing many challenging reactions at relatively low temperatures ...

We report a novel type of electromagnetically induced transparency (EIT) analogue based on metamaterials (MMs) with hybrid structures, in which spiral and cut-wire structures serve as bright-mode resonators with the spoof electric localized surface plasmons and electric dipole resonance. With the simulations and experiments, the EIT analogue generated by the frequency detuning and hybridization between the resonators is verified. The simulated surface charge density and electric and magnetic field distributions, together with the theoretical analysis based on the Lorentz oscillator model, reveal the principle of the EIT analogue. Moreover, the transmission window of the MM demonstrates linear dependence on the refractive index’s change of surrounding media, showing the potential as a tool for environmental detection.

The hot electron transition of noble materials to catalysis accelerated by localized surface plasmon resonances (LSPRs) was detected by in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) in this article. This paper synthesized an Ag Nanowire (AgNW) @ WS2 core-shell structure, with an ultra-thin shell of WS2 (3 ∼ 7 nm), and characterized its photocatalytic properties. The AgNW@WS2 core-shell structure exhibited different surface-enhanced Raman spectroscopy (SERS) effects by changing shell thickness, indicating that the effect of AgNW could be controlled by WS2 shell. Furthermore, the hydrogen production of AgNW@WS2 could reach to 356% of that of pure WS2. The hot electrons arising from the LSPRs effect broke through the Schottky barrier between WS2 and AgNW and transferred to the WS2 shell, whose photocatalytic effect was thus enhanced. In addition, when the LSPRs effect was intensified by reducing the shell thickness, the hot electron transition of noble materials to catalysis was accelerated.

Cadmium telluride (CdTe) thin films with a nanocolumnar morphology were grown on glass substrates using the Sublimated Vapor Effusion Deposition technique and a rotational source in counter-rotation with respect to the substrate. Afterward, it was proceeded to coat with silver nanoparticles whose average size was of ~ 100 ± 40 nm. X-ray diffraction analysis showed that all samples presented the zinc-blend structure with a preferred orientation of (111), with a crystallite size of ~ 52 nm, and that they were under tensile stress. The bandgap value was EG = 1.53 eV and the Urbach energy E0 ~ 13.2 meV. The porosity value was estimated at ~ 0.0562 (5.6%). A Localized Surface Plasmon Resonances effect was presented for the Ag nanoparticles near the wavelengths close to 548 nm and 660 nm, and this resulted in improved light absorption in the CdTe nanocolumnar layer compared to samples grown only with a CdTe nanocolumnar structure.

This paper proposes a novel design of plasmonic perovskite solar cell (PSC). It consists of an anti-reflective glass of fluorine-doped tin oxide (FTO), a compact buffer layer of n-type titanium dioxide (TiO2), an absorbing thin-film layer of perovskite (MAPbI3) integrated with gold (Au) nanospheres, a layer of p-type doped spiro-OMeTAD, and a layer of the cathode on aluminum (Al). This multilayer design’s primary purpose is to allow the light to enter the PSC with the minimum reflection and trap it in the active layer due to the presence of Au nanospheres. In this layer, the higher efficiency of PSC is achieved by localized surface plasmon resonances (LSPRs) in the wavelength range from 300 to 1100 nm. A reflective Al layer is used at the bottom of the device to reflect the light into the upper layers to considerably enhance the PSC absorption. The three-dimensional finite-difference time-domain method was conducted to find the best solution to Maxwell’s equations so that the best thickness and radius can be selected for each layer and Au nanospheres, respectively. Proper physical dimensions and Au nanospheres played a significant role in numerically indicating that the proposed structures are 60% more absorbent than the other conventional PSCs. In-house simulation software is used to approximate the solar cell by applying the finite element method to develop solutions for the drift–diffusion and Poisson’s equations. The examinations of the previous studies revealed that the current study is the first study that has simulated the real model of Auger recombination in perovskite. The results indicated that the proposed PSC embedded with Au nanospheres has the following properties: the built-in potential of 3.16 V, short-circuit current of 27.97 mA/cm2, the open-circuit voltage of 1 V, maximum power of 24.84 mW/cm2, fill-factor of 0.88, the conduction band of 3 eV, electron quasi-Fermi level of 2.5 eV, the hole quasi-Fermi level of 0.6 eV, and efficiency of 24.84%. Finally, the suggested PSC has performed 62% more efficient than conventional PSCs.

It is essential to realize a Raman measurement technique without artifact or fluorescence signals for high-quality and reliable data in a valid molecular-level analysis and interpretation. This requirement applies especially to a molecule with strong fluorescence like porphyrin. Here, the surface of a gold substrate performs better as a DCDR substrate for tetraphenylporphyrin than other surfaces, such as tantalum, indium tin oxide glass, or aluminium. Polarized Raman spectra of tetraphenylporphyrin demonstrated the oriented deposition of porphyrin crystallites on the Au substrate using the drop coating technique. The emission anisotropy suggests that the deposited crystallites are arranged outward radially with the porphyrin ring orientation. The orientation is signed by the NH⋯HN axis that is parallel to the radial vector along the X-axis. Moreover, it also demonstrates high chemical stability after preservation and repeated measurements. The Raman signal on a gold substrate is enhanced more than on other substrates beyond mere preconcentration of analytes or the coffee-ring effect only, which might be due to the contribution of the SERRS effect. This effect will be discussed based on the interactions among localized surface plasmons, vibronic transitions, and Raman active vibrational modes.

Due to the relatively low photo-thermal conversion efficiency and poor tumor targeting capacity, phototheranostic nanoagents encounter some challenges in cancer photothermal therapy. To address this problem, in the current research we developed vacancy-rich MoSe2-x (0 ≤ x ≤ 1) nanoflowers (MNFs) with molecular 2-deoxy-D-glucose (2-DG) as the activity target, which could be used as a novel phototheranostic nanoagent in the photoacoustic imaging guided chemo-photothermal synergistic therapy. This selenium-deficient structure endows MNFs with high photothermal conversion efficiency (41.7%) due to the strong localized surface plasmon resonances. Besides, the surface linked 2-DG molecules and the flower-like morphology in the nanoagents promoted the targeting effect (active and passive), thus facilitating the efficient concentration of the nanoagents within the tumor site. Both in vitro and in vivo anti-tumor experiments have demonstrated the high synergistic efficacy promoted by MNFs and complete tumor eradication with lower administration dosages could be achieved. This rational design of nanoparticles not only provided the paradigm of high therapeutic efficacy of a chemo-photothermal protocol for precise cancer theranostics, but also expanded the scope of nanomedical applications using semiconductor-based nanoplatforms through well-defined designing of their microstructures and physiochemical properties.

Sustainability drives modern technology. Practices ensuring efficient resource utilization, guided resource handling and promotion of negative ecological footprint befittingly implicate “growth”. With manufacturing being one of the major contributing sectors to a nation's economy, adopting greener fabrication processes, the production of cleaner energy and the development of efficient products are important to achieve technological translation. Herein, a bi-functional hybrid (semiconductor–metal) system comprising zinc oxide nano leaves uniformly decorated with gold nano islands was synthesized using a one-step, room temperature biosynthetic reduction strategy. Being a one-step process, the number of reaction reagents and auxiliary byproducts was limited while material engineering ensured efficient product performance derived from coexistence of localized surface plasmon, semiconduction and their synergistic interaction. Detailed characterization of the as synthesized hybrid system concludes presence of defect states, crystalline nature, engineered band gap, pertinent chemical elemental state and interfacial charge distribution features. The hybrid nanostructures show strong surface-enhanced Raman scattering (SERS) characteristics for model R6G molecules (LOD: 10−10 M). Marked with the presence of symmetric and non-totally symmetric Raman vibrations, the role of electromagnetic and chemical enhancement was equally attributed to improved signal strengths. Contribution from charge transfer was verified using off resonance measurements and by studying the photolytic behavior of the nano-hybrid system. The self-cleaning feature of the nanohybrid was tested against a model bacterial contaminant S. aureus, which was killed with 100% efficiency using ∼60 μg ml−1 under natural sunlight.

This review describes recent studies on coupled plasmonic systems for controlling plasmon dynamics and molecular detection using spectral modulations. The plasmon dephasing time can be controlled by weak and strong coupling regimes between the plasmonic nanostructures or localized surface plasmon resonances (LSPRs) and the other optical modes such as microcavities. The modal coupling induces near-field enhancement by extending the plasmon dephasing time to increase the near-field enhancement at certain wavelengths resulting in the enhancement of molecular detection. On the other hand, the interaction between LSPR and molecular excited or vibrational states also modulates the resonance spectrum, which can also be used for detecting a small number of molecules with a subtle change in the spectrum. The spectral modulation is induced by weak and strong couplings between LSPRs and the electronic or vibrational states of molecules, and this method is sensitive enough to measure a single molecule.

Two-dimensional metal carbides and nitrides, known as MXenes, are an emerging class of materials that are promising for a variety of applications. In this work, using time-dependent density functional theory calculations, we investigate the localized surface plasmon resonances and electric field confinement of pristine and surface-terminated [fluorinated (F) and/or oxidized (O)] mono-layered titanium carbide (Ti3C2) MXene nanoclusters. We found that the nanoclusters (Ti48C32, Ti48C32F32, and Ti48C32O32) exhibit broadband photoabsorption spectra and localized surface plasmon resonances even at low energy in the infrared region (a spectral range of interest for molecular sensing). In addition, the nanoclusters produce a sizable electric field confinement on the surface with a strength that varies with the F/O surface termination. Our findings provide significant theoretical insight into the optical and plasmonic properties of MXene nanoclusters.

The development of Surface Enhanced Raman Scattering (SERS) promotes the wide application of Raman spectroscopy in chemical and biomolecular detection. SERS detection relies on analytes in close contact with the metallic surface, and therefore direct molecular trace detection in the liquid phase is difficult. In this paper, static liquid phase SERS detection was performed simply using a capillary without pre-functionalization. Gold nanoparticles (AuNPs) with an optimized size ensure localized surface plasmons in resonance with the exciting laser light. Grazing incidence and multimode interference in the capillary ensure that the longitudinal Raman signal is effectively excited and accumulated. An enhancement factor as high as 108 and a detection limit of 10−9 M of crystal violet in aqueous solution have been achieved.

In this article, we propose an ultra-compact microwave sensor based on an effective localized surface plasmon (ELSP) resonance for complex permittivity measurement of aqueous ethanol solution. The sensitivity of the sensor is dramatically enhanced thanks to the strong electromagnetic (EM) field coupling and enhancement of the ELSP in a deep-subwavelength scale. An equivalent circuit model of the sensor is established for analyzing the sensing mechanism, and the complex permittivity of the aqueous ethanol solution under test is extracted from the S-parameter through an empirical model. For demonstration, we successfully predict the complex permittivity of aqueous ethanol solution with an ethanol concentration of 0%–90% through simulations and experiments. This ELSP-based sensor features an ultra-compact size of $0.008\lambda _{0}^{2}$ and high sensitivity of 0.57% and can find many applications (liquid permittivity measurement, liquid testing, and so on) in highly integrated systems.

Introducing nanostructured metals with ultraviolet plasmonic characters has attracted much attention for fabricating high performance optoelectronic devices in the shorter wavelength spectrum. In this work, platinum nanoparticles (PtNPs) with controlled plasmonic responses in ultraviolet wavelengths were successfully synthesized. To demonstrate the promising availability, PtNPs with desired sizes were deposited on a hexagonal ZnO microwire via Ga-doping (PtNPs@ZnO:Ga MW). Under ultraviolet illumination, typical near-band-edge emission of ZnO:Ga MW was considerably enhanced; meanwhile, the photocurrent is much larger than that of the bare MW. Thereby, the enhanced phenomena of a ZnO:Ga MW is related to localized surface plasmon resonances of the decorated PtNPs. A single MW with a hexagonal cross-section can be a potential platform to construct a whispering gallery mode (WGM) cavity due to its total inner wall reflection. Given this, the influence of PtNPs via ultraviolet plasmons on lasing features of the ZnO:Ga MW was tested. The lasing characteristics are significantly enhanced, including lasing output enhancement, a clear reduction of the threshold and the improvement of the quality factor. To exploit the working principle, PtNPs serving as powerful ultraviolet plasmons can couple with ZnO:Ga excitons, accelerating radiative recombination. Since fabricating stable, typical nanostructured metals with ultraviolet plasmons remains a challenging issue, the results illustrated in the work may offer a low-cost and efficient scheme for achieving plasmon-enhanced wide-bandgap semiconductor based ultraviolet optoelectronic devices with excellent performances.

Shell-isolated nanoparticles (SHINs) have attracted increasing interest for non-interfering plasmonic enhanced sensing in fields such as materials science, biosensing, and in various electrochemical systems. The metallic core of these nanoparticles is isolated from the surrounding environment preventing direct contact or chemical interaction with the metal surface, while still being close enough to enable localized surface plasmon enhancement of the Raman scattering signal from the analyte. This concept forms the basis of the shell isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique. To date, the vast majority of SHIN designs have focused on SiO2 shells around spherical nanoparticle cores and there has been very limited published research considering alternatives. In this article, we introduce a new polymer-based approach which provides excellent control over the layer thickness and can be applied to plasmonic metal nanoparticles of various shapes and sizes without compromising the overall nanoparticle morphology. The SHIN layers are shown to exhibit excellent passivation properties and robustness in the case of gold nanosphere (AuNP) and anisotropic gold nanostar (AuNS) core shapes. In addition, in situ SHINERS spectro-electrochemistry measurements performed on both SHIN and bare Au nanoparticles demonstrate the utility of the SHIN coatings. Correlated confocal Raman and SEM mapping was achieved to clearly establish single nanoparticle SERS sensitivity. Finally, confocal in situ SERS mapping enabled visualisation of the redox related molecular structure changes occurring on an electrode surface in the vicinity of individual SHIN-coated nanoparticles.

The dependence of field splitting characteristics of multilaminar plasmonic structure on its metallic components topology is analyzed. It is found that the coupling interaction between metallic-particle-centered localized surface plasmons generates a collective effect, collective metallic-particles-centered plasmons, to dominantly determine the plasmonic resonances of the structure. When the metallic particles filling ratio within the matrix is high, this collective effect may cause resonance splitting phenomenon and greatly enlarge the frequency range of field splitting enhancement, which is the physical mechanism and also the designing guideline for multilaminar plasmonic broadband perfect absorber. The surface plasmon polaritons are concurrently superimposed on the metallic-particles-centered collective effect to establish an inter-group coupling competition effect, which may strengthen or weaken the preexisting resonance processes through constructive or destructive field interference in between. This serves as the theoretical base for narrowband field splitting enhancement applications. Moreover, we have revealed the existence of the corresponding relationship between the specific field splitting resonance and those participating or dominating metallic particles involved, which provides the advantages to finely tailor field splitting characteristics through precise implantation of nanoparticles.

The absorption and reflection of electromagnetic waves by various particles in the earth’s atmosphere allow the passage of only certain electromagnetic wavelengths to reach the ground, called Earth’s atmosphere transparent window. In this study, perfect absorption was theoretically obtained in the range of near- and mid-infrared earth’s atmospheric transparency window using a simple absorber with metal-dielectric-metal structure. The numerical simulations showed the average absorption to reach 96.2% at wavelengths from 2000 to 6000 nm. Also, the broadband absorption was noticed and attributed to combined physical mechanisms, such as anti-reflection effect, localized surface plasmon polariton, propagating surface plasmon polarization, Fabry–Perot cavity and slow light mode. Meanwhile, the proposed absorber displayed simple-structure, low-cost, wide-angle, and polarization-independent. In sum, the proposed absorber might be useful for future applications related to atmospheric transparency window, such as remote sensing, energy harvesting, infrared detection, and stray light elimination.

Given the sub-wavelength trapping challenges in the optical tweezers, the plasmonic tweezers serve as a bridge by breaking the diffraction limit. Hence, the development of plasmonic tweezers can open up many potential applications in biology, medicine, and chemistry. In this paper, using localized surface plasmons (LSPs) of graphene nanodisk with a resonance frequency of 20 THz, we design a lab-on-a-chip optophoresis system, which can be utilized to effectively trap the nanoparticles. The LSPs of graphene nanodisk generate a large field gradient in the deep sub-wavelength area around the resonance frequency. We show that by an appropriate choice of chemical potentials of the graphene nanodisks, the strong optical near-field forces desired for trapping can be generated under the illumination of the THz source when the polystyrene (PS) nanoparticles are located in the vicinity of graphene nanodisks. Numerical simulations show that the designed system with graphene nanodisks of 250 nm in diameter and chemical potentials of $\mu _{c} = 0.6$ eV can trap the PS nanoparticles of 12 nm in diameter and larger with a THz source intensity of 19 $mW/{\mu } {m^{2}}$ , demonstrating acceptable sensitivities for variations in the nanoparticle diameter and refractive index. Moreover, at the same source intensity, the graphene nanodisks with $\mu _{c} = 0.7$ eV can trap the PS nanoparticle as small as 9.5 nm in diameter.

We present a strong coupling system realized by coupling the localized surface plasmon mode in individual silver nanogrooves and propagating surface plasmon modes launched by periodic nanogroove arrays with varied periodicities on a continuous silver medium. When the propagating modes are in resonance with the localized mode, we observe a √N scaling of Rabi splitting energy, where N is the number of propagating modes coupled to the localized mode. Here, we confirm a giant Rabi splitting on the order of 450-660 meV (N = 2) in the visible spectral range, and the corresponding coupling strength is 160-235 meV. In some of the strong coupling cases studied by us, the coupling strength is about 10% of the mode energy, reaching the ultrastrong coupling regime.

Molecular bond dissociation and formation reactions induced by localized surface plasmons of metal nanostructures are promising reactions in terms of the effective utilization of sunlight. The plas...

Plasmonic materials interact strongly with light to focus and enhance electromagnetic radiation down to nanoscale volumes. Due to this localized confinement, materials that support localized surface plasmon resonances are capable of driving energetically unfavorable chemical reactions. In certain cases, the plasmonic nanostructures are able to preferentially catalyze the formation of specific photoproducts, which offers an opportunity for the development of solar-driven chemical synthesis. Here, using plasmonic environments, we report inducing an intramolecular methyl migration reaction, forming 4-methylpyridine from N-methylpyridinium. Using both experimental and computational methods, we were able to confirm the identity of the N-methylpyridinium by making spectral comparisons against possible photoproducts. This reaction involves breaking a C-N bond and forming a new C-C bond, highlighting the ability of plasmonic materials to drive complex and selective reactions. Additionally, we observe that the product yield depends strongly on optical illumination conditions. This is likely due to steric hindrance in specific regions on the nanostructured plasmonic substrate, providing an optical handle for driving plasmonic catalysis with spatial specificity. This work adds yet another class of reactions accessible by surface plasmon excitation to the ever-growing library of plasmon-mediated chemical reactions.

Infrared detection technology has been widely applied in many areas. Unlike internal photoemission and the photoelectric mechanism, which are limited by the interface barrier height and material bandgap, the research of the hot carrier effect from nanometer thickness of metal could surpass the capability of silicon-based Schottky devices to detect mid-infrared and even far-infrared. In this work, we investigate the effects of physical characteristics of Cr nanometal surfaces and metal/silicon interfaces on hot carrier optical detection. Based on the results of scanning electron microscopy, atomic force microscopy, and X-ray diffraction analysis, the hot carrier effect and the variation of optical response intensity are found to depend highly on the physical properties of metal surfaces, such as surface coverage, metal thickness, and internal stress. Since the contact layer formed by Cr and Si is the main role of infrared light detection in the experiment, the higher the metal coverage, the higher the optical response. Additionally, a thicker metal surface makes the hot carriers take a longer time to convert into current signals after generation, leading to signal degradation due to the short lifetime of the hot carriers. Furthermore, the film with the best hot carrier effect induced in the Cr/Si structure is able to detect an infrared signal up to 4.2 μm. Additionally, it has a 229 times improvement in the signal-to-noise ratio (SNR) for a single band compared with ones with less favorable conditions.

We have discussed the impact on experimental characteristics which are important to detect localized surface plasmon peaks in EELS successfully, namely: the intensity of plasmonic signal, the signal to background ratio, and the signal to zero-loss peak ratio considering a limited dynamic range of the spectrometer camera.

Within a mid-IR few-cycle laser, the generation of MHz isolated attosecond pulses via nanoplasmonic field enhancement in a structure that consisted of a metal coupled nanoparticle-disk, an insulator spacer, and a thin metal film is theoretically investigated. The interaction between the localized surface plasmons caused by the coupled nanodisks and the metal layer results in increased electric field. The resonance wavelengths of these two types of surface plasmons supported by the nanostructure are tailored by changing the coupled nanoparticle-disk size and the material type. Numerical calculations are used to optimize nanostructure and attain plasmonic field enhancement factors up to 86. The HHG process is studied by the time–frequency analysis. Our studies show that only short trajectories contribute to HHG and also, the chirp of these harmonics is very low. As a result, an isolated 40 as pulse without phase compensation is obtained directly by superposing the chirp-free high-order harmonics.

Metallic nanoparticles have been used to harvest energy from a light source and transfer it to adsorbed gas molecules, which results in a reduced chemical reaction temperature. However, most reported reactions, such as ethylene epoxidation, ammonia decomposition and H–D bond formation are exothermic, and only H–D bond formation has been achieved at room temperature. These reactions require low activation energies ( 3.1 eV) can be initiated at room temperature by using localized surface plasmons in the deep-UV range. As an example, by leveraging simultaneous excitation of multiple localized surface plasmon modes of Al nanoparticles by using high-energy electrons, we initiate the reduction of CO2 to CO by carbon at room temperature. We employ an environmental transmission electron microscope to excite and characterize Al localized surface plasmon resonances, and simultaneously measure the spatial distribution of carbon gasification near the nanoparticles in a CO2 environment. This approach opens a path towards exploring other industrially relevant chemical processes that are initiated by plasmonic fields at room temperature. Metallic nanoparticles used to harvest energy from a light source typically result in reduced chemical reaction temperature. Endothermic reactions requiring higher activation energy can now be initiated at room temperature using localized surface plasmons in the deep-UV range.

In this brief, we propose a novel wide-bandpass substrate integrated waveguide (SIW) filter in a compact circular cavity. It is implemented by etching spoof localized surface plasmon (SLSP) structure for more modes excitation. The dominant mode of SIW cavity and the seven modes of SLSP are employed to realize octuple-mode wideband filtering feature. Moreover, the two edges of the filter passband can be adjusted independently by changing the parameters of SIW or SLSP. Compared to traditional SIW wideband filters, the proposed structure dramatically increases the bandwidth meanwhile balances the size, complexity, and loss. A sample was fabricated and measured to validate the design. The measured results are in good agreement with the simulated ones, showing that a 3-dB relative bandwidth about 63% is achieved.

International audience; Localized surface plasmon resonance (LSPR) excitation on the photochromic reaction of a diarylethene derivative (DE) was studied by surface enhanced Raman scattering (SERS). UV and visible light irradiations transform reversibly DE between open-form (OF) and closed-form (CF) isomers, respectively. A mixture of PMMA and DE (either OF or CF isomer) was spin-coated onto gold nanorods (GNRs) arrays, designed by electron beam lithography, with two localized surface plasmon resonances (LSPR) at distinct wavelengths, due to their anisotropy. The photochromic reaction rates from CF to OF isomers, under LSPR excitation, were monitored from SERS spectral changes under different polarizations, on the same GNR substrate to compare the effect of LSPR field strength. It appears that the photoisomerization rate was faster when LSPR was excited with the polarization parallel to the GNR long axis. The present results highlight a potential genuine mechanism, from near field LSPR excitation, involved in the photochromic enhancement of diarylethene photochromes.

Strong coupling between localized surface plasmons and molecular absorptions leads to remarkable changes in the photophysical properties of dye-loaded metal nanoparticles. Here, we report supramolecular nanocomposites consisting of BODIPY, tryptophan, and gold nanoparticles, and investigate the effect of structural variations on their photophysical properties. Our results indicate that the photostability and photosensitization properties of the nanocomposites depend on the chemical composition of the BODIPY molecules. The singlet oxygen quantum yield of the nanocomposites NC1 (BODIPY, B1 bearing a single methyl group) and NC3 (BODIPY, B3 with 5 methyl and 2 iodo groups) were 0.46 and 0.42, respectively, which were significantly higher compared to their individual components. Ultrafast spectroscopy studies revealed that the migration of photoexcited BODIPY electrons to the plasmonic photoexcitation allowed electron transfer into the singlet oxygen states, thereby leading to efficient generation of singlet oxygen.

We prepared MoS2 monolayers on Au nanodot (ND) and nanohole (NH) arrays. Both these sample arrays exhibited enhanced photoluminescence intensity compared with that of a bare SiO2/Si substrate. The ...

Raman/fluorescence microspectroscopic analysis of individual polymer chains and nanobeads dissolved in solution will become a powerful analytical method to study their molecular structure and characteristics. With this motivation, we focused on the use of Raman microspectroscopy for optically trapped soft matter. A tightly focused near-infrared laser beam formed a microassembly of thermoresponsive polymer chains such as poly(N-isopropylacrylamide) due to a local photothermal effect and optical force. By using this method, we developed a technique for determining the polymer concentration in a polymer microassembly. Furthermore, we demonstrated a molecular condensation and detection technique based on microassembly on plasmonic nanostructures. For this molecular condensation and detection process, localized surface plasmons play an essential role in the optical force enhancement and local temperature increase around the plasmonic nanostructures. Finally, aiming toward novel manipulation methods of smaller soft nanomaterials, nanostructured semiconductor-assisted (NASSCA) optical tweezers are introduced. In this paper, we reviewed the optical manipulation methods of polymer chains and nanobeads and their applications in analytical chemistry. We reviewed our recent studies on optical manipulation techniques for microspectroscopic analysis of optically trapped polymers. A focused laser beam exerts an optical force on polymer chains, leading to the microassembly formation of them. We applied the conventional optical tweezers for the concentration determination techniques of phase-separated thermoresponsive polymer chains by combining with microspectroscopies. To overcome the limitations of the conventional optical tweezers, localized surface plasmon has attracted much attention. Finally, we introduced our original manipulation technique based on nanostructured semiconductor-assisted optical tweezers; NASSCA optical tweezers.