Hybrid Au-Ag Research Articles

One-Pot Synthesis of Colloidal Hybrid Au (Ag)/ZnO Nanostructures with the Participation of Maleic Acid Copolymers.

One-pot synthesis of colloidal Au/ZnO and Ag/ZnO nanohybrid structures was carried out. The copolymers of maleic acid-poly(N-vinyl-2-pyrrolidone-alt-maleic acid), poly(ethylene-alt-maleic acid), or poly(styrene-alt-maleic acid) were used as templates for the sorption of cations of metals-precursors and stabilization of the resulting nanoheterostructures. Simultaneous production of two types of nanoparticles has been implemented under mild conditions in an aqueous alkaline medium and without additional reagents. Equimolar ratios of the metal cations and appropriate load on all copolymers were used: molar ratio of maleic acid monomeric units of copolymer/gold (silver)cations/zinc cations was 1/0.15/0.23 (1/0.3/0.15). The process of obtaining the heterostructures was studied using UV-Vis spectroscopy. The kinetics of the formation of heterostructures was influenced by the nature of the maleic acid copolymer and noble metal cations used. A high reaction rate was observed in the case of using zinc and gold cations-precursors and a copolymer of maleic acid with N-vinylpyrrolidone as a stabilizer of nanoparticles. The structure of the synthesized polymer-stabilized heterostructures was studied using instrumental methods of analysis-XPS, FTIR, PXRD, and TEM. Under the conditions used, stable colloidal solutions of heterodimers were obtained, and such structure can be converted to a solid state and back without loss of properties.

Asymmetrical Plasmon Distribution in Hybrid AuAg Hollow/Solid Coded Nanotubes

Morphological control at the nanoscale paves the way to fabricate nanostructures with desired plasmonic properties. In this study, we discuss the nanoengineering of plasmon resonances in 1D hollow nanostructures of two different AuAg nanotubes, including completely hollow nanotubes and hybrid nanotubes with solid Ag and hollow AuAg segments. Spatially resolved plasmon mapping by electron energy loss spectroscopy (EELS) revealed the presence of high order resonator-like modes and localized surface plasmon resonance (LSPR) modes in both nanotubes. The experimental findings accurately correlated with the boundary element method (BEM) simulations. Both experiments and simulations revealed that the plasmon resonances are intensely present inside the nanotubes due to plasmon hybridization. Based on the experimental and simulated results, we show that the novel hybrid AuAg nanotubes possess two significant coexisting features: (i) LSPRs are distinctively generated from the hollow and solid parts of the hybrid AuAg nanotube, which creates a way to control a broad range of plasmon resonances with one single nanostructure, and (ii) the periodicity of the high-order modes are disrupted due to the plasmon hybridization by the interaction of solid and hollow parts, resulting in an asymmetrical plasmon distribution in 1D nanostructures. The asymmetry could be modulated/engineered to control the coded plasmonic nanotubes.

Generation of gold and silver nanoparticles using laser ablation of thin bimetallic films and bulk targets in water

Generation of gold and silver nanoparticles by laser ablation in water without the addition of surfactants is very attractive due to the purity of such nanoparticles. However, such nanoparticles face the problem of long-term stability, which severely limits their applicability. Here, we demonstrate the generation of hybrid gold-silver nanoparticles using the laser ablation of thin-film composites on a glass substrate in water, and compare with the laser fabrication of nanoparticles by using bulk targets of silver and gold. Thin-film method allows the formation of stable hybrid Au–Ag nanoparticles in distilled water without any stabilizers and additional ligands with an opportunity to regulate the nanoparticle composition using different metal ratios, layer order, and thickness of films. The stability and optical properties of the hybrid nanoparticles depend on the used laser pulse energy. This study demonstrates that the thin film method produces nanoparticles with higher stability compared to the bulk target method. These outcomes are encouraging for the creation of better-performing, stable, and clean nanoparticles that can be used in a variety of applications in biomedicine, sensors, integrated circuits, filters, batteries, covid-19 tests, solar cells, dual-energy mammography (DEM), computed tomography (CT), and other components of optical and electronic devices.

Unifying stability and plasmonic properties in hybrid nanoislands: Au–Ag synergistic effects and application in SERS

In plasmon-based devices, the choice of metal for the nanostructures often leads to an undesirable tradeoff between either the superb performance of Ag or the stability of Au. There is a great interest in combining Au and Ag in a way that preserves both their favourable properties, while also exploiting synergistic effects to boost surface-enhanced Raman scattering (SERS) performance beyond the capabilities of a single metal. To address this issue, a large-area nanofabrication procedure based on galvanic replacement was used to create hybrid Au–Ag nanoislands with a diverse morphology and highly tunable (through visible to NIR) plasmon resonance. Their stability was comprehensively studied and shown to be complex to achieve. However, in the right conditions, Au–Ag nanoislands with silver-like plasmonic properties were fabricated, and shown to be stable over a period of at least 5 months. Moreover, their SERS efficiency considerably outperformed even that of Ag nanoislands. Computational investigation helped explain the advantageous properties and provided insights for future sensor design. Detection of the model molecules was achieved in the nanomolar range and in mild conditions (low laser power), indicating great potential for biomedicine sensing. Beyond that, nanoislands with simultaneous stability and good plasmonic properties can find application in a wide variety of photonic devices.

Synthesis and Characterization of Dye-Doped Au@SiO2 Core-Shell Nanoparticles for Super-Resolution Fluorescence Microscopy.

Dye-doped nanoparticles have been investigated as bright, fluorescent probes for localization-based super-resolution microscopy. Nanoparticle size is important in super-resolution microscopy to get an accurate size of the object of interest from image analysis. Due to their self-blinking behavior and metal-enhanced fluorescence (MEF), Ag@SiO2 and Au@Ag@SiO2 nanoparticles have shown promise as probes for localization-based super-resolution microscopy. Here, several noble metal-based dye-doped core-shell nanoparticles have been investigated as self-blinking nanomaterial probes. It was observed that both the gold- and silver-plated nanoparticle cores exhibit weak luminescence under certain conditions due to the surface plasmon resonance bands produced by each metal, and the gold cores exhibit blinking behavior which enhances the blinking and fluorescence of the dye-doped nanoparticle. However, the silver-plated nanoparticle cores, while weakly luminescent, did not exhibit any blinking; the dye-doped nanoparticle exhibited the same behavior as the core fluorescent, but did not blink. Because of the blinking behavior, stochastic optical reconstruction microscopy (STORM) super-resolution analysis was able to be performed with performed on the gold core nanoparticles. A preliminary study on the use of these nanoparticles for localization-based super-resolution showed that these nanoparticles are suitable for use in STORM super resolution. Resolution enhancement was two times better than the diffraction limited images, with core sizes reduced to 15 nm using the hybrid Au-Ag cores.

Laser-deposited hybrid Au-Ag@C nanoparticles as efficient SERS & adsorption material

In this work, we present an approach to the synthesis of hybrid multifunctional nanomaterials with pronounced functional properties (SERS, adsorption properties). One-step laser-induced deposition method was used to synthesize hybrid Au-Ag@C nanoparticles. Physicochemical and functional properties of obtained nanostructures were studied using various experimental techniques. Adsorption properties were studied via Raman spectroscopy using organic chromophore – rhodamine 6G.

Collective effect of hybrid Au-Ag nanoparticles and organic-inorganic cathode interfacial layers for high performance polymer solar cell

The cooperative effect of hybrid Au-Ag nanoparticles and organic-inorganic cathode interfacial layers to advance the power conversion efficiency (PCE) of regio regular (rr) P3HT:PCBM based polymer solar cells (PSCs) are systematically demonstrated. In this work initially, two types of plasmonic nanoparticles (NPs), namely, citrate stabilized gold (AuNPs) and silver (AgNPs) were separately synthesized and then physically blend together with three different volume ratio [AuNPs + AgNPs (25:75), AuNPs + AgNPs (50:50) and AuNPs + AgNPs (75:25)]. These three blended NP solutions were then mixed together in the PEDOT:PSS (20 v/v %) hole extraction layer (HEL) to form three new NPs doped HEL and their effect on the rr-P3HT:PCBM based PSCs were systematically analyzed. For dual organic-inorganic cathode interfacial layers, two organic hole blocking materials, BPhen and BCP were used for enhanced charge collection in combination with LiF:Al as conventional cathode electrode. The collective effect of hybrid NPs with the dual cathode interfacial layers was examined with two varying active polymer blends, rr-P3HT:PC61BM and rr-P3HT:PC71BM. It has been found that the PCE increases considerably for both the active blend systems, with PEDOT:PSS + [AuNPs:AgNPs (25:75)] + BCP:LiF:Al as the modified cathode electrode. This is due to suitable electronic energy level matching of BCP:LiF:Al and active blend with the excellent surface plasmon property of the AuNPs:AgNPs (25:75) in the UV–Visible region compared to AuNPs:AgNPs (50:50) and AuNPs:AgNPs (75:25). Devices having configuration PEDOT:PSS + [AuNPs:AgNPs (25:75)] as HEL, rr-P3HT:PC71BM as active blend and BCP:LiF:Al provided PCE, ɳmax = 5.71% with Jsc = 16.44 mA/cm2, Voc = 0.58 V, FF = 60% and device with rr-P3HT:PC61BM as active blend layer was showing as PCE, ɳmax = 5.31% with Jsc = 14.77 mA/cm2, Voc = 0.58 V and FF = 62% with the same PEDOT:PSS + [AuNPs:AgNPs (25:75)] layer and BCP:LiF:Al. These results conclusively described a very simple technique in which the cooperative effect of plasmonic hybrid metals nanoparticles and dual cathode interfacial layers outstandingly enrich the PCE and in general the complete nature of rr-P3HT:PCBM based PSCs.

Density-matrix evaluation of the enhancement to resonant Raman scattering and fluorescence of molecules confined in metallic nanoparticle dimers

In the present work we study the surface-enhanced resonant Raman scattering (SERRS) and fluorescence (SEF) spectra of a general model molecule confined in metallic dimers consisting of Ag, Au and hybrid AuAg nanoparticles (NPs). The electromagnetic (EM) enhancement factors were simulated by the generalized Mie scatting method and the scattering cross section of the molecules were obtained by density-matrix calculations. The influence of the size of the NPs and the separation between the dimer on the Raman scattering and fluorescence were systematically studied and analyzed in detail. It was found that the SERRS mainly related to EM enhancement and the SEF depended on the competition between EM enhancement and quantum yield, both of which could be controlled by tuning the radius and separation of the metallic dimers. The optimal radius of the NPs for SERRS were found to be around 30 nm for AgNPs, 40 nm for AuNPs and 50 nm for hybrid AuAgNPs. The strongest Raman enhancement as predicted by the theoretical simulations were 6.2 × 1010, 1.5 × 107 and 5.2 × 108 for the three types of structures, respectively. These results could offer valuable information for the design of metallic substrates for surface enhanced Raman and fluorescence measurements.

Hybrid Au-Ag Nanostructures for Enhanced Plasmon-Driven Catalytic Selective Hydrogenation through Visible Light Irradiation and Surface-Enhanced Raman Scattering.

Herein, we report the successful application of hybrid Au-Ag nanoparticles (NPs) and nanochains (NCs) in the harvesting of visible light energy for selective hydrogenation reactions. For individual Au@Ag NPs with Au25 cores, the conversion and turnover frequency (TOF) are approximately 8 and 10 times higher than those of Au25 NPs, respectively. Notably, after the self-assembly of the Au@Ag NPs, the conversion and TOF of 1D NCs were approximately 2.5 and 2 times higher than those of isolated Au@Ag NPs, respectively, owing to the coupling of surface plasmon and the increase in the rate at which hot (energetic) electrons are generated with the formation of plasmonic hot spots between NPs. Furthermore, the surface-enhanced Raman scattering (SERS) activity of 1D Au@Ag NCs was strengthened by nearly 2 orders of magnitude.

Design and simulate the properties of triangular periodic nanoparticle arrays with the structure of bi-layer hexagonal lattice

In this study, the discrete dipole approximation (DDA) method was used to simulate the hybrid bi-layer hexagonal lattice of triangular periodic nanoparticle arrays (PNAs). The PNAs nanophotonic devices could be fabricated with pure silver, but their performances would be easily degenerated because of the oxidation (forming Ag2O) and sulfuration (forming Ag2S). Theoretical results show that the oxidation and sulfuration of Ag thin film lead to a significant red shift in the wavelength to reveal the maximum extinction efficiency (λmax) and to a significant decrease in the maximum peak value of localized surface plasmon resonances (LSPRs). The structures with the bi-layer materials of Ag2O–Ag and Ag2S–Ag were used to prove the degeneration of the properties in the extinction spectra of the LSPRs by using DDA method for simulation. We would find that the maximum peak value of the wavelength of the extinction efficiency spectra critically decreased and λmax had a red shift as the thicknesses of Ag2O and Ag2S increased. The structures with the bi-layer materials of Au–Ag and TiO2–Ag were also used to investigate their extinction spectra of the LSPRs. The simulation results of DDA method found that the maximum peak value of the wavelength of the extinction efficiency spectra slightly decreased as the thicknesses Au and TiO2 increased. Based on the Ag triangular nanostructure, the use of Au and TiO2 to form hybrid Au–Ag and TiO2–Ag triangular nanostructure cannot only be used to put forth of preventing oxidation and sulfuration but have a better performance than the Ag2O–Ag and Ag2S–Ag hybrid triangular nanostructures. Meanwhile, the thicknesses of TiO2 or Au layers could be used to decide the refractive index sensitivity (RIS) and figure of merit (FOM) of the hybrid Au–Ag and TiO2–Ag PNAs.

Generation of Localized Surface Plasmon Resonance Using Hybrid Au-Ag Nanoparticle Arrays as a Sensor of Polychlorinated Biphenyls Detection.

In this study, the hybrid Au–Ag hexagonal lattice of triangular and square lattice of quadrate periodic nanoparticle arrays (PNAs) were designed to investigate their extinction spectra of the localized surface plasmon resonances (LSPRs). First, their simulating extinction spectra were calculated by discrete dipole approximation (DDA) numerical method by changing the media refractive index. Simulation results showed that as the media refractive index was changed from 1.0 to 1.2, the maximum peak intensity of LSPRs spectra had no apparent change and the wavelength to reveal the maximum peak intensity of LSPRs spectra was shifted lower value. Polystyrene (PS) nanospheres with two differently arranged structures were used as the templates to deposit the hybrid Au–Ag hexagonal lattice of triangular and square lattice of quadrate periodic PNAs by evaporation method. The hybrid Au–Ag hexagonal lattice of triangular and square lattice of quadrate PNAs were grown on single crystal silicon (c-Si) substrates, and their measured extinction spectra were compared with the calculated results. Finally, the fabricated hexagonal lattices of triangular PNAs were investigated as a sensor of polychlorinated biphenyl solution (PCB-77) by observing the wavelength to reveal the maximum extinction efficiency (λmax). We show that the adhesion of β-cyclodextrins (SH-β-CD) on the hybrid Au–Ag hexagonal lattice of triangular PNAs could be used to increase the variation of λmax. We also demonstrate that the adhesion of SH-β-CD increases the sensitivity and detection effect of PCB-77 in hexagonal lattice of triangular PNAs.

Laser-induced transformation of supramolecular complexes: approach to controlled formation of hybrid multi-yolk-shell Au-Ag@a-C:H nanostructures.

In the present work an efficient approach of the controlled formation of hybrid Au–Ag–C nanostructures based on laser-induced transformation of organometallic supramolecular cluster compound is suggested. Herein the one-step process of the laser-induced synthesis of hybrid multi-yolk-shell Au-Ag@a-C:H nanoparticles which are bimetallic gold-silver subnanoclusters dispersed in nanospheres of amorphous hydrogenated a-C:H carbon is reported in details. It has been demonstrated that variation of the experimental parameters such as type of the organometallic precursor, solvent, deposition geometry and duration of laser irradiation allows directed control of nanoparticles’ dimension and morphology. The mechanism of Au-Ag@a-C:H nanoparticles formation is suggested: the photo-excitation of the precursor molecule through metal-to-ligand charge transfer followed by rupture of metallophilic bonds, transformation of the cluster core including red-ox intramolecular reaction and aggregation of heterometallic species that results in the hybrid metal/carbon nanoparticles with multi-yolk-shell architecture formation. It has been found that the nanoparticles obtained can be efficiently used for the Surface-Enhanced Raman Spectroscopy label-free detection of human serum albumin in low concentration solution.

Effect of Refractive Index of Substrate on Fabrication and Optical Properties of Hybrid Au-Ag Triangular Nanoparticle Arrays

In this study, the nanosphere lithography (NSL) method was used to fabricate hybrid Au-Ag triangular periodic nanoparticle arrays. The Au-Ag triangular periodic arrays were grown on different substrates, and the effect of the refractive index of substrates on fabrication and optical properties was systematically investigated. At first, the optical spectrum was simulated by the discrete dipole approximation (DDA) numerical method as a function of refractive indexes of substrates and mediums. Simulation results showed that as the substrates had the refractive indexes of 1.43 (quartz) and 1.68 (SF5 glass), the nanoparticle arrays would have better refractive index sensitivity (RIS) and figure of merit (FOM). Simulation results also showed that the peak wavelength of the extinction spectra had a red shift when the medium’s refractive index n increased. The experimental results also demonstrated that when refractive indexes of substrates were 1.43 and 1.68, the nanoparticle arrays and substrate had better adhesive ability. Meanwhile, we found the nanoparticles formed a large-scale monolayer array with the hexagonally close-packed structure. Finally, the hybrid Au-Ag triangular nanoparticle arrays were fabricated on quartz and SF5 glass substrates and their experiment extinction spectra were compared with the simulated results.

Enhancement of surface enhanced raman scattering from arrays of hybrid Au–Ag nanoparticles via localised surface plasmon resonance

The enhancement of surface enhanced raman scattering of the hybrid Au–Ag triangular nanostructure arrays via localised surface plasmon resonance is systematically investigated. The hybrid nanostructure can prevent the pure silver nanoparticles from oxidation and the stability of Au–Ag nanoparticles compared with non-coated Ag nanoparticles has been verified. Discrete dipole approximation calculated results show the size of the nanoparticle has an important effect on localised surface plasmon resonance of the hybrid nanostructure. Nanosphere lithography is used to fabricate the hybrid nanoparticle arrays with different sizes of nanoparticle. Both theoretical calculations and experimental results show that with an increase in size of the nanoparticle, positions of localised surface plasmon resonance peak are less strongly redshifted and peak of the surface enhanced Raman scattering of the arrays is obviously strengthened. A maximum intensity of the surface enhanced raman scattering can be achieved when the localised surface plasmon resonance wavelength of the hybrid Au–Ag nanoparticle arrays well match the laser excitation wavelength.

基底折射率对金银复合纳米阵列的制备及光学性能的影响

基底折射率对金银复合纳米阵列的制备及光学性能的影响

Sensitivity of Triangular Hybrid Au–Ag Nanostructure Array

The sensitivity is one of the most important parameters in the sensing field. Silver triangular nano- structure array is the traditional substrate for detecting the targets. In this paper, we proposed triangular hybrid Au-Ag nanostructure array to be optimized substrate for nanobiosensor. Effort was made to study sensitivity of triangular hybrid Au-Ag nanostructure array through finite-difference time-domain (FDTD) algorithm-based computational numerical calculation method. The extinction efficiency was obtained by theoretical numerical calculation. It is found that the triangular hybrid Au-Ag nanostructure array possess the refractive index sensitivity of 273 nm/RIU when thickness of silver is 40 nm and the gold is 10 nm, and refractive index of the medium is around 1.33. It is higher than the pure silver nanostructure array (242 nm/RIU). Copyright © 2010 American Scientific Publishers. All rights reserved.

Plasmonic Lenses: A Review

Four types of plasmonic lenses for the purpose of superfocusing designed on the bases of approximate negative refractive index concept, subwavelength metallic structures, waveguide mode were introduced, and curved chains of nanoparticles, respectively, were introduced. Imaging mechanism, fabrication, and characterization issues were presented. Theoretical analyses of the illumination with different polarization states on focusing performance of the plasmonic lenses were given also. In addition, a hybrid Au-Ag plasmonic lens with chirped slits for the purpose of avoiding oxidation of Ag film was presented.

Numerical Design Methods of Nanostructure Array for Nanobiosensing

Numerical methods are very important for designing nanodevices since localized surface plasmon resonance is sensitive to the geometric parameters. Especially, as for nano-biosensor, the proper choice of design tool is very critical in terms of the accuracy and simulation time. In this paper, we compare the discrete dipole approximation (DDA) with the finite integration technique (FIT) of the full-wave electromagnetic commercial software (CST Microwave Studio) in worldwide use with popularity. The refractive index sensitivity of rhombic hybrid Au–Ag nanostructures is calculated and compared in visible wavelength using DDA and FIT. Comparing the calculated results, the DDA has two advantages over the FIT: easy control of geometric parameter and less simulation time without compromising the accuracy. The limitations of the DDA will be deliberated as well.

Optical Characteristics of Rhombic Hybrid Au–Ag Nanostructures Calculated by Discrete Dipole Approximation Method

The extinction spectra of rhombic hybrid Au–Ag nanostructures have been calculated using the discrete dipole approximation (DDA) aided design method. The plasmon peaks of the rhombic hybrid Au–Ag nanostructures can be tuned not only by the structural parameters but also by the effective refractive index of the medium surrounding around the nanostructures. The relationship between the extinction efficiency and the polarizations of the incident light are also analyzed by the DDA method. Based on the calculated curves, the main parameters of the nanostructure arrays such as thickness, period and the refractive index sensitivity can be determined. Using this aided method, a hybrid Au–Ag nanostructures array is designed with the determinant parameters of thickness (Au 5 nm, Ag 25 nm), period (400 nm) and the refractive index sensitivity (400 nm/RIU). This study shows that the particle material, period and the effective refractive indexes of the mediums have significant effect on the optical properties of the nanostructures, and DDA aided design method can provide the perfect structure parameters for our hybrid nanostructures. Copyright © 2010 American Scientific Publishers All rights reserved

Hybrid Au-Ag subwavelength metallic structures with variant periods for superfocusing

Yongqi Fu School of Physical Electronics, University of Electronic Science and Technology of China, No. 4, Section 2, North Jianshe Road, Chengdu, Sichuan Province 610054 China Wei Zhou Precision Engineering and Nanotechnology Center, School of Mechanical and Aerospace Engineering, Nanyang Technological University and Institute of High Performance Computing, Singapore, 639798 Singapore A hybrid Au-Ag subwavelength metallic zone plate-like structure was put forth for the purpose of preventing oxidation and sulfuration of Ag film, as well as realizing superfocusing. The Au film acts as both a protector and modulator in the structure. Focusing performance is analyzed by means of three-dimensional finite-difference and time-domain (FDTD) algorithm-based computational numerical calculation. It can be tuned by varying thicknesses of both Au and Ag thin films. Our calculation results show that thickness difference between the Au and Ag thin films plays an important role for transmission spectra. Ratio of Au to Ag film thicknesses, hAu/hAg is proportional to the relevant peak transmission intensity. In case of hAuhAg=50 nm, both transmission intensity and focusing performance are improved. In addition, the ratio hAu/hAg strongly influences position of peak wavelengths Au and Ag generated from beaming through the metallic structures.