Layers Of Metal Nanoparticles Research Articles

Ag@Au yolk shells decorated onto silica spheres for enhanced plasmonic applications

Silica surfaces covered with a homogenous layer of metal nanoparticles exhibit superior plasmonic properties when compared with pristine colloidal counterparts, as they have higher scattering probability with enhanced potential utility. Precise galvanic replacement reactions performed on such sacrificial templates are of great interest. Herein, we demonstrate the robust formation of Ag@Au yolk shells decorated onto the dielectric silica spheres via a direct one-step galvanic replacement procedure, evidently initiating the deposition of Au onto low surface energy Ag facets (prefixed onto the silica spheres), resulting in a disjointed framework of compact dealloyed metal lobes, wherein their facets remain smooth enough with a high degree of crystallinity and exhibit maximal porosity. Our combined spectroscopic data analyses corroborate the plausible mechanism governing solely the formation of Ag@Au core-shell onto the silica spheres rather than their hollow counterparts. Furthermore, we made the respective monolayer films using the well-known air-water interface self-assembly technique, which allowed us to easily decorate different substrates with a uniform array of these surface-coupled metal nanoparticles. Enhanced refractive index (RI) sensing applications based on the sensitivity and FOM (figure of merit) calculations demonstrate the versatile nature of our synthetic protocol for direct synthesis of optical metamaterials along with their intriguing light-matter interactions, in general. Also, the plasmonic vector field of 2-D assembled nanoparticle monolayer displays intrigued SERS enhancement of crystal violet dye when compared with their respective drop-casted films, thus establishing a novel method for producing diverse meta-structures based efficient SERS substrates with promising applications in ultrasensitive chemical and biological sensing.

Multilayer Plasmonic Nanostructures for Improved Sensing Activities Using a FEM and Neurocomputing-Based Approach.

In order to obtain optimized elementary devices (photovoltaic modules, power transistors for energy efficiency, high-efficiency sensors) it is necessary to increase the energy conversion efficiency of these devices. A very effective approach to achieving this goal is to increase the absorption of incident radiation. A promising strategy to increase this absorption is to use very thin regions of active material and trap photons near these surfaces. The most effective and cost-effective method of achieving such optical entrapment is the Raman scattering from excited nanoparticles at the plasmonic resonance. The field of plasmonics is the study of the exploitation of appropriate layers of metal nanoparticles to increase the intensity of radiation in the semiconductor by means of near-field effects produced by nanoparticles. In this paper, we focus on the use of metal nanoparticles as plasmonic nanosensors with extremely high sensitivity, even reaching single-molecule detection. The study conducted in this paper was used to optimize the performance of a prototype of a plasmonic photovoltaic cell made at the Institute for Microelectronics and Microsystems IMM of Catania, Italy. This prototype was based on a multilayer structure composed of the following layers: glass, AZO, metal and dielectric. In order to obtain good results, it is necessary to use geometries that orthogonalize the absorption of light, allowing better transport of the photocarriers—and therefore greater efficiency—or the use of less pure materials. For this reason, this study is focused on optimizing the geometries of these multilayer plasmonic structures. More specifically, in this paper, by means of a neurocomputing procedure and an electromagnetic fields analysis performed by the finite elements method (FEM), we established the relationship between the thicknesses of Aluminum-doped Zinc oxide (AZO), metal, dielectric and their main properties, characterizing the plasmonic propagation phenomena as the optimal wavelengths values at the main interfaces AZO/METAL and METAL/DIELECTRIC.

Fabrication and Characterization of Functionalized Multi-Wall Carbon Nanotubes Flexible Network Modified by a Layer of Polypyrrole Conductive Polymer and Metallic Nanoparticles

Short Multi-Walled Carbon Nanotubes functionalized with OH group (MWCNTs-OH) were used to synthesize flexible MWCNTs networks. The MWCNTs suspension was synthesized using Benzoquinone (BQ) and N, N Dimethylformamide alcohol (DMF) in specific values and then deposited on filter paper by filtration from suspension (FFS) method. Polypyrrole (PPy) conductive polymer doped with metallic nanoparticles (MNPs) prepared using in-situ chemical polymerization method. To improve the properties of the MWCNTs networks, a coating layer of (PPy) conductive polymer, PPy:Ag nanoparticles, and PPy: Cu nanoparticles were applied to the network. The fabricated networks were characterized using an X-ray diffractometer (XRD), UV-Vis. spectrometer, and Atomic Force Microscope (AFM). XRD results revealed that the broadening for the (002) peak decreased after being coated with PPy and increased for the doped samples with MNPs, indicating on decrease in the crystalline size (MWCNTs/PPy) sample and increasing for doped ones with Ag and Cu MNPs. AFM images revealed that the surface roughness of the MWCNTs-OH network decreased after being coated with PPy, PPy: Ag, and PPy: Cu. With the help of AFM and XRD results, the CNTs contain 14 layers, while the inner and outer diameters were 18.2 nm and 27 nm receptivity. The UV-Vis. spectrum of MWCNTs showed several peaks, the highest in the 350 nm range. The coated of MWCNTs greatly affected the absorption spectrum, with many bands appearing between 300 to 450 nm and increasing the absorbance along the overall spectrum. For samples doped with Ag NPs and Cu NPs, a weak absorption peak of the plasmonic resonance frequency of the metallic nanoparticles. Analysis of Raman spectra shows that (ID/IG) ratios for all networks are less than one, which prove that the fabricated networks have few impurities and have good homogeneity. This work aimed to synthesize and characterize a flexible MWCNTs network and develop it by coated with a layer of conductive polymer and metallic nanoparticles for gas sensing application using quick and straightforward preparation methods.

Disordered-nanoparticle-based etalon for ultrafast humidity-responsive colorimetric sensors and anti-counterfeiting displays.

The development of real-time and sensitive humidity sensors is in great demand from smart home automation and modern public health. We hereby proposed an ultrafast and full-color colorimetric humidity sensor that consists of chitosan hydrogel sandwiched by a disordered metal nanoparticle layer and reflecting substrate. This hydrogel-based resonator changes its resonant frequency to external humidity conditions because the chitosan hydrogels are swollen under wet state and contracted under dry state. The response time of the sensor is ~104 faster than that of the conventional Fabry-Pérot design. The origins of fast gas permeation are membrane pores created by gaps between the metal nanoparticles. Such instantaneous and tunable response of a new hydrogel resonator is then exploited for colorimetric sensors, anti-counterfeiting applications, and high-resolution displays.

AlCrO protected textured stainless-steel surface for high temperature solar selective absorber applications

The diffusion of substrate material into absorbing layer and oxidation of metal substrate or cermet metal nanoparticles at high temperatures are known as inevitable problems of the solar selective absorbers. In this study, we consider the use of textured stainless steel (SS) surface coated with a protective AlCr oxide layer as a high temperature solar selective absorber. The textured SS surface was prepared by ion etching techniques and AlCr oxide protective layer was deposited by RF magnetron sputtering. The absorptivity and emissivity of the as-prepared absorbers were 0.86–0.92 and 0.151–0.168, respectively. In order to evaluate the thermal stability, the absorbers were annealed at 600–800 °C for different time in ambient atmosphere. Absorbers demonstrated a red shift of the onset of the reflectivity at all annealing temperatures. The high activation energy of 315 kJ/mol was calculated. In terms of thermal stability, the service lifetime of the absorbers at 500 °C was estimated to be about 100 years and at 700 and 800 °C the absorbers were stable at least 50 and 1 h, respectively. A detailed examination of the annealed absorber surface revealed growth of surface Mn3O4 nanocrystals, which resulted in observed change of the reflectance spectra, while the textured surface morphology had no significant change. The results show that the protective textured surface has much higher thermal stability in air than iron-based cermet absorbers.

Experimental detection of Immunoglobulin G by prism-coupled angular interrogation and a support vector machine

A typical prism-coupled surface-plasmon-resonance biosensor comprises a metal thin film in contact with a solution containing an analyte to be sensed. The metal film also acts as a binding surface for bioreceptor molecules to capture and concentrate the analyte molecules of interest. We investigated the use of a porous, anisotropic, periodically non-homogeneous material called a chiral sculptured thin film (CSTF) grown on top of the metal film to confine the solution in its pores. The efficacy of a basic plasmonic sensor was compared with those of two types of sensors containing a CSTF, one type having a metal-nanoparticle layer at a distance of one period from the metal film and the other without that layer. The chosen analyte was Immunoglobulin G and the chosen bioreceptor was Protein A. Measurements were made over a wide angular range rather than over a small range tied to the excitation of a surface-plasmon-polariton wave, and the collected data were used to train a machine-learning algorithm called a support vector machine for classification. We concluded that the metal/CSTF sensor with a metal-nanoparticle layer performs best, the metal-nanoparticle layer being crucial to its better performance.

Highly ordered arrays of hat-shaped hierarchical nanostructures with different curvatures for sensitive SERS and plasmon-driven catalysis.

Regulation of hot spots exhibits excellent potential in many applications including nanolasers, energy harvesting, sensing, and subwavelength imaging. Here, hat-shaped hierarchical nanostructures with different space curvatures have been proposed to enhance hot spots for facilitating surface-enhanced Raman scattering (SERS) and plasmon-driven catalysis applications. These novel nanostructures comprise two layers of metal nanoparticles separated by hat-shaped MoS2 films. The fabrication of this hybrid structure is based on the thermal annealing and thermal evaporation of self-assembled polystyrene spheres, which are convenient to control the metal particle size and the curvature of hat-shaped nanostructures. Based on the narrow gaps produced by the MoS2 films and the curvature of space, the constructed platform exhibits superior SERS capability and achieves ultrasensitive detection for toxic molecules. Furthermore, the surface catalytic conversion of p-nitrothiophenol (PNTP) to p, p'-dimercaptobenzene (DMAB) was in situ monitored by the SERS substrate. The mechanism governing this regulation of hot spots is also investigated via theoretical simulations.

On-demand nanoparticle-on-mirror (NPoM) structure for cost-effective surface-enhanced Raman scattering substrates

We report a robust technique to fabricate a cost-efficient Raman substrate which is composed of polyvinylpyrrolidone (PVP) coated gold nanoparticles layer on commercial aluminum foil. The layer of metal nanoparticles on the aluminum foil, i.e., the nanoparticle-on-mirror (NPoM) structure was fabricated by spraying nanoparticle colloidal solution directly on the foil. The detection limit (LOD) of NPoM substrate is investigated by performing the SERS for Rhodamine 6G (R6G) with the concentration ranging from mM to nM without any post treatment of the substrate. The findings show that the LOD of 1 nM and maximum intensity enhancement factor of ~ 24 is accomplished. Field enhancement owing to reflection from the metallic mirror is the reason behind the signal enhancement and it would be beneficial for routine clinical applications, trace chemical detection, and disease diagnostics.

Understanding the sintering and heat dissipation behaviours of Cu nanoparticles during low-temperature selective laser sintering process on flexible substrates

In this paper, a facile method was introduced to fabricate fine conductive patterns by low-temperature selective laser sintering of Cu nanoparticles. By virtue of a nanosecond-pulsed ultraviolet laser source, fine circuits with a thickness of ∼8 μm and a conductivity of 3–6.5 × 106 S m−1 was successfully fabricated from Cu nanoparticle paste with a high metal content >80 wt.% on a flexible substrate at a wide scan rate range of 5–500 mm s−1. The sintered circuits exhibited a special sandwich morphology, with fully melted features in the centre and thermally sintered neck-connected features on the edges. A twofold linear relationship between the width of thermally sintered region and the reciprocal of the laser scan rate was revealed, indicating a heat dissipation mode transition from metal layer dominated dissipation to substrate dominated dissipation with the decrease of the laser scan rate. Finite element simulations were carried out to study the evolutions of temperature field and heat dissipation with changing laser scan rate and power, and the results fitted well with experimental results. On this basis, a relational expression was further proposed to determine the optimal processing window for laser sintering of metal nanoparticle layers. Our method extends the producible thickness and improves the fabrication efficiency of laser-printed circuits with desirable conductivity. The findings of this study can provide a guidance for understanding and controlling the sintering and heat transfer process of printing methods with similar materials and techniques.

A Layer-by-Layer Assembly Route to Electroplated Fibril-Based 3D Porous Current Collectors for Energy Storage Devices.

Electrical conductivity, mechanical flexibility, and large electroactive surface areas are the most important factors in determining the performance of various flexible electrodes in energy storage devices. Herein, a layer-by-layer (LbL) assembly-induced metal electrodeposition approach is introduced to prepare a variety of highly porous 3D-current collectors with high flexibility, metallic conductivity, and large surface area. In this study, a few metal nanoparticle (NP) layers are LbL-assembled onto insulating paper for the preparation of conductive paper. Subsequent Ni electroplating of the metal NP-coated substrates reduces the sheet resistance from ≈103 to <0.1 Ωsq-1 while maintaining the porous structure of the pristine paper. Particularly, this approach is completely compatible with commercial electroplating processes, and thus can be directly extended to electroplating applications using a variety of other metals in addition to Ni. After depositing high-energy MnO NPs onto Ni-electroplated papers, the areal capacitance increases from 68 to 811 mFcm-2 as the mass loading of MnO NPs increases from 0.16 to 4.31 mgcm-2 . When metal NPs are periodically LbL-assembled with the MnO NPs, the areal capacitance increases to 1710 mFcm-2 .

Carbide-Modified Pd on ZrO2 as Active Phase for CO2-Reforming of Methane—A Model Phase Boundary Approach

Starting from subsurface Zr0-doped “inverse” Pd and bulk-intermetallic Pd0Zr0 model catalyst precursors, we investigated the dry reforming reaction of methane (DRM) using synchrotron-based near ambient pressure in-situ X-ray photoelectron spectroscopy (NAP-XPS), in-situ X-ray diffraction and catalytic testing in an ultrahigh-vacuum-compatible recirculating batch reactor cell. Both intermetallic precursors develop a Pd0–ZrO2 phase boundary under realistic DRM conditions, whereby the oxidative segregation of ZrO2 from bulk intermetallic PdxZry leads to a highly active composite layer of carbide-modified Pd0 metal nanoparticles in contact with tetragonal ZrO2. This active state exhibits reaction rates exceeding those of a conventional supported Pd–ZrO2 reference catalyst and its high activity is unambiguously linked to the fast conversion of the highly reactive carbidic/dissolved C-species inside Pd0 toward CO at the Pd/ZrO2 phase boundary, which serves the role of providing efficient CO2 activation sites. In contrast, the near-surface intermetallic precursor decomposes toward ZrO2 islands at the surface of a quasi-infinite Pd0 metal bulk. Strongly delayed Pd carbide accumulation and thus carbon resegregation under reaction conditions leads to a much less active interfacial ZrO2–Pd0 state.

Fabrication of metal-dielectric nanocomposites using a table-top ion implanter

A miniature low-voltage vacuum spark is an effective facility for creating composite layers in a dielectric matrix, including metal clusters, which have numerous optical applications. The results of studies of the optical characteristics of alkali-halide crystals (LiF and KCl) irradiated with beams of accelerated metal ions, which are emitted by a small-sized, low-voltage (2.5 kV) and low-energy (10 J) vacuum spark and a high-voltage (50 kV) pulsed ion implanter are presented. In both cases, composite layers of metal nanoparticles and/or molecular clusters are formed at submicrometer depth when irradiating these crystals. The low voltage implant method produces similar optical effects as seen in crystals processes at much higher energies. This result shows the possibility of creating a desktop metal ion implanter for various applications.

Electrochemically Reduced Graphene Oxide – Noble Metal Nanoparticles Nanohybrids for Sensitive Enzyme-Free Detection of Hydrogen Peroxide

Electrochemically reduced graphene oxide (ERGO) is a versatile material for the electrode modification, which enables modification of the physicochemical properties of the surface by the reduction and reoxidation of oxygen groups. The oxygen functional groups and structural defects of ERGO deposited on a layer of metal nanoparticles facilitate the electron transport and enhance the electrocatalytic properties of the nanoparticles. ERGO layers show moderate-intrinsic electrocatalytic properties towards the electrochemical reduction of hydrogen peroxide. In this contribution, we present studies of ERGO layers on the top of the nanoparticle layer composed of gold nanoparticles stabilized with silicotungstate ligands (Au/SiW12), silver nanoparticles stabilized with silicotungstate ligands (Ag/SiW12), and silver nanoparticles stabilized with phosphomolybdate ions (Ag/PMo12). The nanoparticles are prepared by the reduction of the chloroauric acid or silver nitrate by the partially reduced forms of H4SiW12O40 or H3PMo12O40 acid. The films of nanoparticles are conditioned by the repetitive potential cycling at pH = 6 before the deposition of the graphene oxide (GO) layer. The GO layer is reduced by scanning the potential between − 0.4 and − 1.2 V vs. SCE. Combination of ERGO with Au/SiW12 or Ag/SiW12 nanoparticles results in synergistic enhancement of amperometric responses to hydrogen peroxide. The electrocatalytic current values observed for the NPs-ERGO layers are higher than the sum of the current for the pure NPs layers and the ERGO layer deposited on a glassy carbon electrode. The Ag/PMo12 nanoparticles show poor electrocatalytic currents due to possible formation of aggregate structures. Infrared and Raman spectroscopies are applied to investigate the electrocatalytic layers.

Mechanochemical synthesis of carbon-stabilized Cu/C, Co/C and Ni/C nanocomposites with prolonged resistance to oxidation

Metal-carbon nanocomposites possess attractive physical-chemical properties compared to their macroscopic counterparts. They are important and unique nanosystems with applications including in the future development of nanomaterial enabled sensors, polymer fillers for electromagnetic radiation shields, and catalysts for various chemical reactions. However, synthesis of these nanocomposites typically employs toxic solvents and hazardous precursors, leading to environmental and health concerns. Together with the complexity of the synthetic processes involved, it is clear that a new synthesis route is required. Herein, Cu/C, Ni/C and Co/C nanocomposites were synthesized using a two-step method including mechanochemical treatment of polyethylene glycol and acetates of copper, nickel and cobalt, followed by pyrolysis of the mixtures in an argon flow at 700 °C. Morphological and structural analysis of the synthesized nanocomposites show their core-shell nature with average crystallite sizes of 50 (Cu/C), 18 (Co/C) and 20 nm (Ni/C) respectively. The carbon shell originates from disordered sp2 carbon (5.2–17.2 wt.%) with a low graphitization degree. The stability and prolonged resistance of composites to oxidation in air arise from the complete embedding of the metal core into the carbon shell together with the presence of surface oxide layer of metal nanoparticles. This approach demonstrates an environmentally friendly method of mechanochemistry for controllable synthesis of metal-carbon nanocomposites.

On the Theory of Plasmon–Excitons: An Estimate of the Coupling Constant and the Optical Spectrum

The structure of the optical spectra related to the resonant interaction of quasi-two-dimensional excitons and localized plasmons is investigated theoretically. The constant of plasmon–exciton coupling is estimated in a model considering a semiconductor quantum well close to a layer of metal nanoparticles in an adjacent dielectric medium. Numerical calculations carried out for GaAs/Ag and ZnO/Al nanosystems indicate that near the plasmon–exciton resonance the spectrum features a double-peak structure which exhibits the plasmon-excitonic anticrossing behavior upon detuning from exact resonance.

Boosting the efficiency of quasi two-dimensional perovskite solar cells via an interfacial layer of metallic nanoparticles

Quasi two-dimensional (Quasi-2D) layered perovskites show higher stability with respect to three-dimensional (3D) perovskites. And compared with two-dimensional (2D) perovskites, quasi-2D perovskites exhibit an improvement in power conversion efficiency (PCE) of perovskite solar cells (PSCs) due to reduced exciton binding energy. So far, different strategies have been adopted to increase PCEs of the quasi-2D PSCs by forming high crystalline quasi-2D perovskite films. In this work, we show that the performance of the quasi-2D aromatic phenylethylammonium based PSCs can be improved greatly through interfacial engineering, i.e., by introducing a layer of SiO2 coated AuAg-alloyed nanoprisms ([email protected]2) before coating the active layer. As a result, the short circuit current density and PCE increased by 32.8% and 34.1%, respectively. Morphological studies show that the incorporated [email protected]2 particles can serve as inducers for forming highly smooth quasi-2D perovskite film. Comprehensive studies indicate that [email protected]2 can also reduce the series resistance, increase light absorption, induce the photon recycling scheme, and assist exciton dissociation at the interface. The combination of all these helpful effects contributes to the observed PCE improvement of quasi-2D PSCs. Our results provide novel insight into the effect of metallic nanoparticles on the quasi-2D perovskite film and on the performance of quasi-2D PSCs.

К теории плазмон-экситонов: оценка константы взаимодействия и оптический спектр

AbstractThe structure of the optical spectra related to the resonant interaction of quasi-two-dimensional excitons and localized plasmons is investigated theoretically. The constant of plasmon–exciton coupling is estimated in a model considering a semiconductor quantum well close to a layer of metal nanoparticles in an adjacent dielectric medium. Numerical calculations carried out for GaAs/Ag and ZnO/Al nanosystems indicate that near the plasmon–exciton resonance the spectrum features a double-peak structure which exhibits the plasmon-excitonic anticrossing behavior upon detuning from exact resonance.

Shear-Assisted Laser Transfer of Metal Nanoparticle Ink to an Elastomer Substrate.

Selective laser sintering of metal nanoparticle ink is an attractive technology for the creation of metal layers at the microscale without any vacuum deposition process, yet its application to elastomer substrates has remained a highly challenging task. To address this issue, we introduced the shear-assisted laser transfer of metal nanoparticle ink by utilizing the difference in thermal expansion coefficients between the elastomer and the target metal electrode. The laser was focused and scanned across the absorbing metal nanoparticle ink layer that was in conformal contact with the elastomer with a high thermal expansion coefficient. The resultant shear stress at the interface assists the selective transfer of the sintered metal nanoparticle layer. We expect that the proposed method can be a competent fabrication route for a transparent conductor on elastomer substrates.

Photoacoustic Generation with Surface Noble Metal Nanostructures

Thin layers of noble metal (Ag, Au) nanoparticles on the surface of optical fiber edge are studied from the viewpoint of photoacoustic fiber-optic generation. In this paper we present theoretical investigation of laser radiation absorbtion by the monolayer of noble metal nanoparticles deposited on the surface of the optical fiber edge. Different nanostructures on the edge of the optical fiber are proposed for effective photoacoustic generation based on lasers with wavelength of 405, 445, 450, 510–530 nm.

Spectroscopy of Plasmon-Excitons in Semiconductor-Metal Nanostructures

The results of the theory considering mixed plasmon-excitonic modes and their spectroscopy are presented. The plasmon-excitons are formed owing to strong Coulomb coupling between quasi-two-dimensional excitons of a quantum well and dipole plasmons of nanoparticles. The effective polarizability associated with a nanoparticle is calculated in a self-consistent approximation taking into account the local field determined by in-layer dipole plasmons and their image charges due to the excitonic polarization of a near quantum well. The spectra of elastic scattering and specular reflection of light are investigated in cases of a single silver nanoparticle and a monolayer of such particles situated in close proximity to a quantum well GaAs/AlGaAs. The optical spectra show a two-peak structure with a deep and narrow dip in the resonant range of plasmon-excitons. Propagation of plasmon-excitonic polaritons is discussed for periodic superlattices whose unit cell consists of a quantum well and a layer of metal nanoparticles. The superradiance regime originating in the Bragg diffraction of plasmon-excitonic polaritons by the superlattice is investigated. It is shown that the broad spectrum of plasmonic reflection depending on the number of unit cells in a superlattice also has a narrow dip at the exciton frequency.