Resonance Plasma Research Articles

Fine-tuning of plasmonics by Au@AuY/Au core–shell nanoparticle monolayer for enhancement of third-order nonlinearity

The manipulation of plasmonics on noble metal nanoparticles (NPs) is of great interest in developing nonlinear photonic devices, such as all-optical switches and frequency combs. An Au@AuY-core/Au-shell nanoparticle (Au@AuY/Au NP) monolayer is proposed for the fine-tuning of plasmonics and enhanced third-order nonlinearity. Based on the different thermodynamic mechanisms of Au and Y ions, the compact Au@AuY/Au core–shell architectures are designed and surface-modified in fused silica (SiO2) with enhanced free electron density, mobility, and quantum size effect. The flexible modulation of plasmonics is realized, resulting in significant absorption enhancement (165% for interband absorption and 38% for free electron absorption, respectively) and fine-tuning of the localized surface plasma resonance (LSPR) band. In addition, the physical mechanism is investigated by density functional theory (DFT) and Mie theory, which reveals a transition from size-independence to size-dependence of LSPR owing to the synergistic effect of multiple physical factors such as free electron density and mobility. With the above advantages, the third-order nonlinearity is enhanced by 4.4 times compared with traditional Au NPs. It indicates the significant potential of Au@AuY/Au core–shell NP monolayer in the performance improvement of nonlinear photonic devices.

Chiral induction enhanced photocatalytic degradation of methyl orange by Ag@Ag3PO4 and the reaction mechanism

A novel chiral Ag@Ag3PO4-NaDC composite was synthesized by chiral induction. SEM, XRD, CD spectrum, FTIR, UV–vis and XPS were used to study the physical and chemical properties of the materials, and the photocatalytic oxidation ability was evaluated with methyl orange as the target pollutant. The results show that the introduction of chirality can obviously promote the light absorption ability, broaden the band gap, enhance the oxidation ability, promote the separation of electrons and holes, greatly enhance the plasma resonance effect of silver nanoparticles, and promote the synergistic effect between silver nanoparticles and silver phosphate. Compared with Ag@Ag3PO4, the catalytic degradation ability of chiral Ag@Ag3PO4-NaDC is improved by more than 60%. Therefore, the chiral Ag@Ag3PO4-NaDC composite exhibits excellent photocatalytic performance. In the degradation of methyl orange by Ag@Ag3PO4-NaDC, a large amount of ·O2- and h+ were formed on the surface, which was the main reason for the oxidation ability.

In situ construction of rich oxygen vacancy Bi/Bi3TaO7 heterojunction photocatalysts

Oxygen vacancy-rich Bi/Bi3TaO7 binary nanomaterials were obtained by a simple in situ reduction. The as-prepared composite exhibited superior photocatalytic activity for the degradation of RhB compared to the single material under the visible light range. The degradation rate of the optimal sample reached 92% within 120 min, 12.25 times that of the pure Bi3TaO7. XRD and HRTEM characterization showed that the Bi metal obtained through in situ reduction was loaded on the Bi3TaO7 nanostructure. In addition, XPS and EPR indicated a significant increase in the oxygen vacancy content of the composites. The time-resolved transient fluorescence spectroscopy and photocurrent results proved that the separation rate of photoexcited carriers and the corresponding ability of photoelectrons are greatly increased. It is due to the synergistic effect of the unique photo-reaction excitation pathway induced by bismuth metal plasma resonance and oxygen vacancies, which not only extends the photo-reaction to the infrared region but also increases the carrier residence time, and this is the fundamental reason for the excellent photocatalytic performance of the composite material. The h+ is the main reactive radical of the reaction, and •O2− also plays a role. Based on the above characterization study, we propose a possible photoreaction mechanism for the synergistic oxygen vacancy and Bi metal of Bi/Bi3TaO7.

Mott‐Schottky Heterostructure Photocatalysis of Ag/h‐BN/Bi2O3 for Water Pollutants Degradation

AbstractThe Ag/h‐BN/Bi2O3 ternary composite was facilely fabricated via self‐assembly combined with in situ reduction. Characterization results showed that the as‐prepared Ag/h‐BN/Bi2O3 possessed distinct surface plasma resonance (SPR) and Mott‐Schottky heterostructure, resulting in significant enhancement of catalytic activity for RhB removal, the reaction rate constant (2.26×10−2 min−1) is 2.5 times that of h‐BN/Bi2O3 under visible‐light irradiation for 2 hours, which was mainly ascribed to the SPR and Mott‐Schottky heterostructure result in Ag/h‐BN/Bi2O3 enhanced visible‐light harvesting capacity and the effectual spatial separation of photoinduced carriers. The quenching process of reactive species indicated that h+ and ⋅O2− play dominant role in the degradation for pollutants. This work demonstrates that Ag/h‐BN/Bi2O3 is a promising stability photocatalyst for water purification.

Nitrogen deficient porous C3N4 on carbon cloth as photoanode with enhanced photoelectrocatalytic activity in hydrogen production

Photoelectrochemical water splitting is an effective way to convert solar energy into hydrogen energy. In this manuscript, Pt-loaded nitrogen-deficient C3N4 was firmly grown on carbon cloth as a photoanode for efficiently photoelectrocatalytic (PEC) water splitting to produce hydrogen. The PEC activity of C3N4 was increased from 0 (C3N4 powder) to 2.45 mmol/h/m2. The performance was further improved to 13.49 mmol/h/m2 after the loading of Pt nanoparticles. The significant improvement in PEC performance can be summarized as the following points: (a) Carbon cloth as substrate enhanced the conductivity of C3N4 and further facilitated photogenerated charges' transfer, (b) enhanced optical absorption and emerged more active edges due to nitrogen defects and porous structures, (c) improved charge transfer and separation efficiency and increased specific surface area at nitrogen-deficient active sites, (d) Pt nanoparticles with local surface plasma resonance (LSPR) effect absorbed more optical electrons and enhanced the rate of electron transport. Therefore, Pt-NCN-CC exhibited great potentials as a photoanode for highly efficient hydrogen production.

Biosensors Based on Gold Nano-Clusters

The world is entering an era of strong infectious diseases, and it is urgent to develop a new type of rapid, efficient detection system. This graph specifically illustrates the detection function of the gold nanoparticles, and the gold nanoparticles-based sensor. Gold-based nanoclusters (NCs) which has a small particle size, has a high degree of stability and no impact on the biological activity. Gold-based NCs has a surface plasma resonance effect and produces visible color, which can be detected by observing the color change using the agglomeration reaction of the detected substance with Gold-based NCs. In order to specifically detect certain biomolecules, some functional groups or small DNA molecular chains of nanolodin are usually modified on it to have a selective detection capability. In the review, we introduce a total of four nano-gold applications, for bacteria, viruses, DNA and cancer, also, respectively elaborating some recent Gold-based NCs detection applications.

Influence of the dielectric constant and thickness of metasurface on terahertz frequency based on plasma resonance

Terahertz modulators possess fascinating physical properties, which is widely used in medical imaging, signal communication and security detection. However, the highprecision control and frequency shift of terahertz wave is still limited in the application field of terahertz devices. Here we propose a metasurface with a cube structure, and the control and frequency shift of terahertz wave are realized by the increase of relative dielectric constant and thickness of the cube structure. The results show that the terahertz frequency response peak of metasurface structure is red shifted, when the dielectric constant of cube structure is increased from 6 to 12.94. Meanwhile, the thickness of the cube structure has an effect on the red shift of the reflection frequency of the terahertz superstructure. When the thickness of the surface material is increased from 1 μm to 3 μm. the reflectance coefficient peak of super surface structure is blue shifted from 11.2 THz to 11.6 THz. This method may be used in advanced applications that need to control electromagnetic waves, such as perfect absorber and smart sensor components.

Studies on the Optical Dispersion Parameters and Electronic Polarizability of Cadmium Sulphide Thin Film

Thin film of Cadmium Sulphide (CdS) was deposited onto a precleaned transparent glass substrate by chemical bath deposition technique from a bath containing Cadmium acetate, ammonium acetate, thiourea and ammonium hydroxide. The deposition time was varied from 10 minutes to 50 minutes at an interval of 20 minutes keeping the bath at a constant temperature of using 78HW-1 constant magnetic stirrer. CdS thin film was characterized by UV-Visible spectrophotometer within the wavelength range of 280 nm – 920 nm using Single – Beam Helios Omega UV – VIS spectrophotometer. The optical parameters; extinction coefficient, refractive index and dielectric constant of CdS thin film were analyzed from the absorption spectra and were found to be affected by the deposition time. The optical band gap energy was obtained by Tauc’s equation and were found to decrease from 3.78 eV – 3.70 eV as the deposition time increases. The dispersion parameters (dispersion energy , oscillation energy , moment of optical dispersion spectra and , static dielectric constant and static refractive index ) were calculated using theoretical Wemple-DiDomenico model. The result show that only and behaved differently but other parameters increase as the deposition time increases. The oscillator strength , oscillator wavelength , high frequency dielectric constant and high frequency refractive index were calculated using single Sellmeier oscillator model. While behaved differently other parameters increase as the deposition time increased. Also, Lattice dielectric constant , N/m* and plasma resonance frequency were equally obtained. While decrease with increase in deposition time, N/m* increase with deposition time. The electronic polarizability of CdS thin film was estimated by Lorenz - Lorentz equation and Clausius Mossotti local field polarizability model. The value is an indication that the films showed good response on the application of photon energy. However, its response reduces as the deposition time increases.

Photothermal‐Responsive Crosslinked Liquid Crystal Polymers

AbstractCrosslinked liquid crystal polymers (CLCPs) are a promising type of smart polymer material with excellent two‐way shape memory behavior under the stimulation of various external conditions. Among the various external stimuli, light with the advantages of instantaneity, high accuracy, remote controllability, pollution‐free, etc., has been widely used in the control of CLCPs. Traditional photoresponsive CLCP systems based on photoisomerization are limited by the penetration depth of ultraviolet light, the number of useful photochemical reactions, and long‐term stability. Recently, a strategy for designing photoresponsive CLCPs based on the photothermal effect has attracted scientific attention. Photothermal materials in the CLCP matrix can convert light into heat through plasma resonance or energy transition under the light irradiation of a certain wavelength, and locally heat the CLCP matrix to beyond the liquid crystal‐to‐isotropic phase transition temperature, thus achieving reversible macroscopic deformation. Combining photothermal materials and CLCPs can decrease the dependence on specific photosensitive groups such as azobenzene mesogens and endow photoresponsive CLCPs with design flexibility. Herein, the photothermal‐responsive CLCPs under the stimulations of different light wavelengths and their application fields are reviewed. In addition, the current challenges in the field of photothermal‐responsive CLCPs are summarized, and a brief outlook on future development is proposed.

Experimental Study of Dual-Parameter SPR Sensor With Integrated Sensing Channel

In order to meet the actual requirements for sensor miniaturization and integration, we propose a compact dual-parameter surface plasma resonance (SPR) fiber sensor, which can simultaneously measure the refractive index and temperature of liquid. The sensor is composed of input-output couplers and two sensing arms. The no-core fibers (NCFs) and microstructured optical fiber (MOF) with deposited films are used as input-output couplers and sensing arms, respectively. One sensing arm is the MOF with silver film for refractive index measurement, and another is that with silver film and PDMS for temperature measurement. Numerical simulation results show its cladding mode is more advantageous in stimulating the SPR effect. Experimental results demonstrate the maximum sensitivity of liquid refractive index is 4139 nm/RIU in the range of 1.333-1.365, and that of liquid temperature is 4.7 nm/°Cin the range of 20-70 °C. The compact structure makes the proposed sensor unique and has a promising application in refractive index and temperature monitoring.

Mycosynthesis of Silver Nanoparticles and Evaluation as Insecticidal Against the Sunn Pest Eurygaster testudinaria in Vitro

Fungi are used to synthesize metal nanoparticles such as silver nanoparticles (AgNPs) because of their specifications as lower toxicity and eco-friendly behavior. Extracellular mycosynthesis of Lecanicillium lecanii silver nanoparticles (AgNPs) was performed, which was done by a redox reaction, where the filtrate crude of L. lecanii acts as a reducing and stabilizing agent for the formation of nanoparticles. The green synthesized AgNPs were evaluated as insecticidal against the adults of sunn pest Eurygaster testudinaria. The AgNPs were characterized by ultraviolet-visible (UV–vis) spectroscopy, Fourier transform infrared (FITR) spectroscopy, X-ray diffraction (XRD), and Field Emission Scanning Electron Microscopy (FESEM). The UV–Vis spectroscopy showed a characteristic absorption peak at 418.5 nm due to surface plasma resonance. FESEM analysis showed that synthesized AgNPs were semi-spherical with an average size of 39.45 nm. The AgNPs showed strong activity in mortality of adults of E. testudinaria under conditions during different periods of time to recorded 100% at concentration 100 ppm compared with 0.00% in control treatment after 10 days from treatment.

Analytical Description of Cyclotron Plasma Resonances in Monolayer Graphene

Analytical Description of Cyclotron Plasma Resonances in Monolayer Graphene

Plasma resonance enhanced electric field and adsorption properties of Ag nanowire based triangular @ circle dimer structures

Plasma resonance enhanced electric field and adsorption properties of Ag nanowire based triangular @ circle dimer structures

In vitro investigation of silver nanoparticles synthesized using Gracilaria veruccosa – A seaweed against multidrug resistant Staphylococcusaureus

In recent years, the biosynthesis of silver (Ag) nanoparticles has attracted a great deal of interest for applications in biomedicine and bioremediation. In the present study, Gracilaria veruccosa extract was used to synthesize Ag nanoparticles for investigating their antibacterial and antibiofilm potentials. The color shift from olive green to brown indicated the synthesis of AgNPs by plasma resonance at 411 nm. Physical and chemical characterization revealed that AgNPs of 20–25 nm sizes were synthesized. Detecting functional groups, such as carboxylic acids and alkenes, suggested that the bioactive molecules in the G. veruccosa extract assisted the synthesis of AgNPs. X-ray diffraction verified the s purity and crystallinity of the AgNPs with an average diameter of 25 nm, while DLS analysis showed a negative surface charge of −22.5 mV. Moreover, AgNPs were tested in vitro for antibacterial and antibiofilm efficacies against S. aureus. The minimum inhibitory concentration (MIC) of AgNPs against S. aureus was 3.8 μg/mL. Light and fluorescence microscopy proved the potential of AgNPs to disrupt the mature biofilm of S. aureus. Therefore, the present report has deciphered the potential of G. veruccosafor the synthesis of AgNPs and targeted the pathogenic bacteria S. aureus.

A multifunctional broadband polarization rotator based on reflective anisotropic metasurface

In this paper, both linear cross-polarization conversion (CPC) and linear-to-circular or circular-to-linear polarization conversion based on a single reflective anisotropic metasurface are realized and experimentally demonstrated. The multifunctional CPC metasurface in the frequency range of 5.9-6.4 GHz and 8.7-17.7 GHz has a fractional band of 68.2%, and the efficiency reaches almost 100% under plasma resonance. In addition, the metasurface acts as a high efficiency circular-polarizer in the range of 6.7–8.4 GHz. Moreover, the polarization transforming functionality of the structure is stable for the change of incident angle for both x-polarized or transverse-electric (TE) and y-polarized or transverse-magnetic (TM) illumination up to 45∘. It can be seen that the anticipated hypersurface has potential applications in reflector antenna, satellite communication and radar.

Enhanced Photocatalytic Degradation of Indoor Low Concentration Gaseous Formaldehyde by Asymmetric Silveriodate Composited with 2D or 3D Bismuth Oxybromide.

Formaldehyde is one of the most hazardous and typical indoor VOCs air pollutants. Asymmetric AgIO3 was respectively composited with 3D hierarchically structured BiOBr and 2D BiOBr nanosheets to photodegrade gas-phase formaldehyde. Ag/AgIO3 /BiOBr(CMC) demonstrated better photocatalytic performance than Ag/AgIO3 /BiOBr owning to the role of biomass solvent sodium carboxymethyl cellulose in increasing the specific surface area, reducing the band gap and changing the dominant facets. Moreover, Ag nanoparticles coming from the reduction in AgIO3 were confirmed by XRD, SEM and XPS. The surface plasma resonance effect of Ag NPs improved the efficiency of the light quantum. Besides, different exposed facets of {010} in BiOBr(CMC) and {001} in BiOBr resulted in distinct oxygen vacancy structures. could be generated via a two-electron transfer pathway on the {010} dominant facets surface in AABR-CMC, leading to the change in photolysis pathway and facilitating more · OH produced by AABR-CMC. Compared with pure AgIO3 and BiOBr or BiOBr(CMC), the photocatalytic efficiency of the composites was improved significantly. Optimal photodegradation efficiency for HCHO was achieved for AABR-75 and AABR-CMC50.

Double enzyme mimetic activities of multifunctional Ag nanoparticle-decorated Co3V2O8 hollow hexagonal prismatic pencils for application in colorimetric sensors and disinfection

Since the catalytic activity of most nanozymes is still far lower than the corresponding natural enzymes, there is urgent need to discover novel highly efficient enzyme-like materials. In this work, Co3V2O8 with hollow hexagonal prismatic pencil structures were prepared as novel artificial enzyme mimics. They were then decorated by photo-depositing Ag nanoparticles (Ag NPs) on the surface to further improve its catalytic activities. The Ag NPs decorated Co3V2O8 (ACVPs) showed both excellent oxidase- and peroxidase-like catalytic activities. They can oxidize the colorless 3,3’,5,5’-tetramethylbenzidine rapidly to induce a blue change. The enhanced enzyme mimetic activities can be attributed to the surface plasma resonance (SPR) effect of Ag NPs as well as the synergistic catalytic effect between Ag NPs and Co3V2O8, accelerating electron transfer and promoting the catalytic process. ACVPs were applied in constructing a colorimetric sensor, validating the occurrence of the Fenton reaction, and disinfection, presenting favorable catalytic performance. The enzyme-like catalytic mechanism was studied, indicating the chief role of ⋅O2- radicals in the catalytic process. This work not only discovers a novel functional material with double enzyme mimetic activity but also provides a new insight into exploiting artificial enzyme mimics with highly efficient catalytic ability.

Ag quantum dots decorated ultrathin g-C3N4 nanosheets for boosting degradation of pharmaceutical contaminants: Insight from interfacial electric field induced by local surface plasma resonance

The design of photocatalysts that can generate local surface plasmon resonance effect (LSPR) is expected to be an effective strategy for improving photocatalytic activity. However, the photocatalytic mechanism of interfacial electric field induced by quantum dot plasma is still unclear. Herein, different amount of Ag quantum dots was loaded on ultrathin carbon nitride sheets (Ag/UCN) to construct Schottky junction. The 1:1 Ag/UCN Schottky junction exhibits excellent photocatalytic activity in ofloxacin degradation with 95.2% removal, and is highly stable during four consecutive photocatalytic cycles. Ag/UCN can also effectively mineralize ofloxacin with 65.8% TOC removal, and NH4+, F− and NO3− were detected in the degradation solution of ofloxacin. Moreover, Ag/UCN shows high antibacterial activity and is effective in pharmaceutical wastewater treatment. The enhanced visible-light absorption of Ag/UCN nanocomposites is attributed to the LSPR effect of Ag quantum dots. Finite difference time domain (FDTD) simulations, density functional theory (DFT) calculations and surface potential confirm that the interfacial electric field drives the photogenerated carriers to cross the Schottky barrier, thus effectively accelerating the electron transfer rate at Ag/UCN interface. The photocatalytic mechanism of the interfacial electric field induced by LSPR effect was also revealed, which provides a new insight for design of LSPR-promoted photocatalyst with interfacial electric field induced by quantum dots.

Two-Dimensional Plasmons in Laterally Confined 2D Electron Systems.

The collective oscillations of charge density (plasmons) in conductive solids are basic excitations that determine the dynamic response of the system. In infinite two-dimensional (2D) electron systems, plasmons have gapless dispersion covering a broad spectral range from subterahertz to infrared, which is promising in light-matter applications. We discuss the state-of-the-art physics of 2D plasmons, especially in confined 2D electron systems in stripe and disk geometry, using the simplest approach for conductivity. When the metal gate is placed in the vicinity of the 2D electron system, an analytical description of the plasmon frequency and damping can be easily obtained. We also analyze gated plasmons in the disk when it was situated at various distances from the gate, and discuss in detail the nontrivial behavior of the damping. We predict that it is not a simple sum of the radiative and collisional dampings, but has a nonmonotonic dependence on the system parameters. For high-mobility 2D systems, this opens the way to achieve the maximal quality factor of plasma resonances. Lastly, we discuss the recently discovered near-gate 2D plasmons propagating along the laterally confined gate, even without applied bias voltage and having gapless dispersion when the gate has the form of a stripe, and discrete spectrum when the gate is in the form of disk. It allows for one to drive the frequency and spatial propagation of such plasmons.

Controllable Preparation of Gold Nanocrystals with Different Porous Structures for SERS Sensing.

Porous Au nanocrystals (Au NCs) have been widely used in catalysis, sensing, and biomedicine due to their excellent localized surface plasma resonance effect and a large number of active sites exposed by three-dimensional internal channels. Here, we developed a ligand-induced one-step method for the controllable preparation of mesoporous, microporous, and hierarchical porous Au NCs with internal 3D connecting channels. At 25 °C, using glutathione (GTH) as both a ligand and reducing agent combined with the Au precursor to form GTH-Au(I), and under the action of the reducing agent ascorbic acid, the Au precursor is reduced in situ to form a dandelion-like microporous structure assembled by Au rods. When cetyltrimethylammonium bromide (C16TAB) and GTH are used as ligands, mesoporous Au NCs formed. When increasing the reaction temperature to 80 °C, hierarchical porous Au NCs with both microporous and mesoporous structures will be synthesized. We systematically explored the effect of reaction parameters on porous Au NCs and proposed possible reaction mechanisms. Furthermore, we compared the SERS-enhancing effect of Au NCs with three different pore structures. With hierarchical porous Au NCs as the SERS base, the detection limit for rhodamine 6G (R6G) reached 10-10 M.