Ag Nanospheres Research Articles

Ag-Modified LiMn2O4 Cathode for Lithium-Ion Batteries: Coating Functionalization

In this work, the properties of silver-modified LiMn2O4 cathode materials are revisited. We study the influence of calcination atmosphere on the properties of the Ag-coated LiMn2O4 (Ag/LMO) and highlight the silver oxidation. The effect of the heat treatment in vacuum is compared with that in air by the characterization of the structure, specific surface area, Li transport properties and electrochemical performance of Ag/LMO composites. Surface analyses (XPS and Raman spectroscopy) show that the nature of the coating (~3 wt.%) differs with the calcination atmosphere: Ag/LMO(v) calcined in vacuum displays Ag nanospheres and minor AgO content on its surface (specific surface area of 4.1 m2 g−1), while Ag/LMO(a) treated in air is mainly covered by the AgO insulating phase (specific surface area of 0.6 m2 g−1). Electrochemical experiments emphasize that ~3 wt.% Ag coating is effective to minimize the drawbacks of the spinel LiMn2O4 (Mn dissolution, cycling instability, etc.). The Ag/LMO(v) electrode shows high capacity retention, good cyclability at C/2 rate and capacity fade of 0.06% per cycle (in 60 cycles).

Modeling, design, and synthesis of gram-scale monodispersed silver nanoparticles using microwave-assisted polyol process for metamaterial applications

High-yield monodispersed silver (Ag) nanospheres were modeled, designed, and synthesized by microwave-assisted (MW-assisted) polyol method from AgNO 3 , polyvinyl pyrrolidone (PVP), and ethylene glycol (EG), as precursors, at 145 °C within a short reaction time of 2 min, and the results were compared to those of conventional polyol method. Maintaining the PVP:AgNO 3 molar ratio, the effect of increasing the amounts of AgNO 3 and PVP at a constant amount of EG (40 mL) on the final product was evaluated. The synthesized nanoparticles (NPs) were characterized by SEM, UV–Vis spectroscopy, FTIR and DLS analysis. The results showed that with increasing the amount of AgNO 3 to 0.5 and 1 g, monodispersed Ag nanoparticles (Ag NPs) with particle sizes of 54 and 61 nm were formed, as per the plasmon absorption peaks at 436 and 442 nm, respectively. Moreover, using 40 mL of the EG solution, we could obtain a high yield of the NPs (~90%). The sub-gram yield was excellently high, offering great opportunities for commercializing the procedure. Also, the proposed study paves a new way for Ag NPs realization for different practical applications ranging from MW to optics. • Mathematical description of the electromagnetic and thermal interaction obtained between the impinging waves and AgNPs. • New MW-assisted polyol process used to synthesized very high yield AgNPs. • The obtained yield corresponded to a significant fraction of a gram as well as higher degrees of monodispersity.

Theoretical and experimental investigations of plasmonic properties of Ag nanosphere and SiO2/Ag core-shell nanostructure

Due to localized surface plasmon resonance (LSPR) properties of plasmonic nanostructures, the electric field is enhanced in their vicinity which is exploited for sensing. Here, the LSPR properties of an Ag nanosphere and a SiO2/Ag core-sell are theoretically studied and their characteristics are experimentally investigated. The theoretical study of the nanostructures showed one intensive plasmon mode whereas only SiO2/Ag core-shell showed the tunable plasmonic properties so that it can be tuned to the desired spectral region by changing core-shell design and the refractive index of the surrounding medium. Optimized SiO2/Ag core-shell showed significant LSPR sensitivity up to 523.6 nm/RIU. SiO2/Ag core-shells were prepared using modified Stöber method. By controlling the reaction conditions, nanoparticles with the size of ~50 nm were fabricated without using a coupling agent, based on the mixture of silver ions in solution including water, ethanol and ammonia, for the direct synthesis of SiO2/Ag core-shells with no aggregation.

Observation of Fano resonance in silver nanocube–nanosphere dimer

In this paper, we perform a theoretical investigation of the plasmon coupling in silver (Ag) nanocube–nanosphere dimer using finite difference time domain (FDTD) technique. Due to plasmonic Fano resonance, we observe a pronounced dip in the absorption spectrum, which is induced by the destructive interference between the bright dipole mode from the Ag nanocube and the dark quadrupole mode from the Ag nanosphere. We study the effects on the Fano resonance by varying the dimensions of the nanocube and nanosphere, as well as the inter-surface gap distance between them. In addition, we vary the local dielectric environment surrounding the dimer and find a wide tuning in the Fano resonance line-shape. We calculate the localised surface plasmon resonance (LSPR) sensitivity of the nanocube–nanosphere dimer to the surrounding environment and find a high figure of merit (FOM) of 32.23, which indicates its promising potential as a plasmonic biosensor.

Durable metal-enhanced fluorescence flexible platform by in-situ growth of micropatterned Ag nanospheres

Here, we demonstrate an in-situ growth of micropatterned silver nanospheres (Ag NS) array on transparent polyimide (PI), namely PI-Ag substrate, applied as a flexible platform for metal-enhanced fluorescence (MEF). The scheme proposed here can easily control the grid formation of Ag NSs and the particle size inside, thus achieving patterned fluorescence imaging and MEF efficiency optimization. Meanwhile, the magnitude of enhanced intensity, relying on the distance between Ag NSs and emissive molecules, was systematically investigated by exploring diverse polyethyleneimine (PEI) spacer thickness. Consequently, an optimal enhancement factor of 7.9 and a pattern of grid fluorescence imaging was obtained with an insertion of 10 nm PEI on the PI-Ag (25 nm) platform. Moreover, owing to robust adhesion between Ag NSs and PI film by in-situ growth, this flexible PI-Ag MEF platform maintained a stable MEF efficiency even after taking mechanical bending for 1000 cycles. This new surface-confined micropatterned Ag NSs PI film provides a promising candidate in design flexible MEF platforms for future analytical and clinical sensing applications.

Effect of Size-Dependent Damping on Plasmon-Hybridized Modes of Asymmetric Nanosphere Dimers: the Role of Nanogap, Size Ratio, Surrounding Medium, and Substrate

Herein, we report quasi-static theory-based simulations on size-asymmetric Au and Ag nanosphere dimers in which size-dependent damping induced by the electron-surface interaction is prominent. The sensitivity of plasmon-hybridized modes of both asymmetric nanodimers with respect to the size ratio of the nanospheres forming nanodimer, the refractive index of surrounding medium, nanogap, and the local dielectric perturbation in the surrounding medium in the presence of the semi-infinite substrate is studied systematically. In each case, the theoretical sensitivity value is estimated for parallel and perpendicular polarizations. Moreover, for comparison, the dependence of plasmon modes of size-symmetric nanosphere dimers on the size-dependent damping is investigated.

Remarkable SERS Detection by Hybrid Cu2O/Ag Nanospheres.

Cu2O nanospheres (NSs) were synthesized by modifying the glucose reduction method. Based on this method, Cu2O/Au (Ag) NSs were further prepared by in situ reduction of HAuCl4 (via electron beam evaporation of Ag). With Rhodamine 6G (R6G) as probe, the surface-enhanced Raman scattering (SERS) characteristics of the three samples were systematically studied. The experiment results showed that the enhancement factor (EF) of Cu2O/Au (Ag) NSs as 1.25 × 108 (2.74 × 109) and the ultralow detection limit (LOD) as 8.07 × 10–12 (1.13 × 10–13) M for R6G. The excellent performance of SERS may be due to the charge transfer (CT) between metal–semiconductor (MS) molecules and the strong electromagnetic field (E-field) of each hot spot. In addition, discrete dipole approximation (DDA) simulations were performed to simulate the E-field enhancement of the Cu2O and Cu2O/Au (Ag) NSs in a three-dimensional (3D) configuration. These further supported that the high SERS performance for R6G is because of the powerful E-field coupling between neighboring Au (Ag) NPs and the surface plasmon resonance (SPR) effect. The Cu2O/Ag NSs have potential in applications such as biomedicine, food safety, and environmental monitoring because of their high sensitivity and good reproducibility.

Mono-dispersed Ag/Graphene nanocomposite as lubricant additive to reduce friction and wear

The unique structure and excellent mechanical property endow silver/graphene nanocomposite with great potential in many lubrication fields. However, its easy aggregation, poor dispersibility and complex synthesis procedures have long been a headache. Herein, we report a simple and effective one-step laser irradiation strategy to fabricate a silver/graphene nanocomposite, which effectively avoids the aggregation and enjoys a good dispersion stability. Structural investigation confirms that mono-dispersed silver (Ag) nanospheres evenly grow on the layered graphene sheets, and this regularly laminated structure further guarantee enhanced lubricating effect. Tribological experiments demonstrate that 0.1 wt% addition of this composite could readily reduce the friction coefficient and wear spot diameter by 40% and 36%, respectively. Detailed lubricating mechanism experiments demonstrate that self-lubrication induced by such layered structure, the change from sliding friction to rolling friction, and the self-repair effect due to Ag nanospheres synergistically contribute to the excellent lubricating performance. More importantly, in comparison with commercial lubricant additives, such Ag/graphene nanocomposites exhibit better lubricating effect and contain no metal corrosion and environmental pollution elements. This study demonstrates that laser irradiation is a powerful strategy to prepare unique layered composite materials for promising lubricant additive to reduce friction and wear.

Optical resonance enhanced Cs activated nano-structured Ag photocathode

Metallic photocathodes have drawn attention due to their outstanding performances of ultrafast photoelectric response and long operational lifetime. However, due to their high work function and the large number of scattering events, metallic photocathodes typically are driven by ultraviolet laser pulses and characterized by low intrinsic quantum efficiency (QE). In this work, a new type of Mie-type silver (Ag) nano-sphere resonant structure fabricated on an Ag/ITO composite substrate is used to enhance the photocathode QE, where Mie scattering resonance is used to enhance the local density of optical state and then to improve the light absorption and electron transporting efficiency in Ag nano-spheres. The cesium (Cs) activation layer is also used to lower the electron work function and then to excite photoemission in the visible waveband for Ag photocathode. The optical characteristics of Ag nano-sphere arrays are analyzed by using finite difference time domain method. For the investigated Ag nano-sphere array, theoretical results show that Mie-type electric dipole resonance modes can be obtained over the 400–600 nm waveband by adjusting the sphere diameter, and the large resonance-enhanced absorption can be achieved in nanospheres at the resonance wavelength. The Ag nano-spheres are fabricated on the Ag/ITO substrate by magnetron sputtering and annealing process, then the Cs activation layer is deposited on surface, and finally QE is measured in an ultra-high vacuum test apparatus. Experimental results show that over 0.35% of QE is obtained for Ag nano-sphere particle (with a diameter of 150 nm) at a wavelength of 425 nm, and the wavelength positions of QE maxima are in agreement with Mie resonance for corresponding geometry predicted from the computational model. Given these unique optoelectronic properties, Ag nanophotonic resonance structured photocathodes represent a very promising alternative to photocathodes with flat surfaces that are widely used in many applications today.

Effects of different structural parameters and the medium environment on plasmonic lattice resonance formed by Ag nanospheres on SiO2 nanopillar arrays

The effects of the diameter of SiO2 nanopillars, the diameter of Ag nanospheres, the arrays’ period, and the medium environment on the plasmonic lattice resonance (PLR) formed by Ag nanospheres on SiO2 nanopillar arrays are systematically investigated. Larger diameters of SiO2 nanopillars with other parameters kept constant will widen the PLR peak, redshift the PLR wavelength, and weaken the PLR intensity. Larger diameters of Ag nanospheres with other parameters kept constant will widen the PLR peak, redshift the PLR wavelength, and strengthen the PLR intensity. Larger array periods or larger refractive index of medium environment corresponds to larger PLR wavelengths.

Broadband anti-reflection in Si substrate via Ag nanospheres on Si nanopillar arrays

A structure of Ag nanospheres on Si nanopillar arrays which sit on a Si substrate is presented to obtain a broadband low reflection. The simulated results show that the average reflection can reach 2.66% in the wavelength range of 400–1100 nm due to the forward scattering effects of Ag nanospheres and the antireflective effects of Si nanopillars, much lower than that of Ag nanosphere arrays on Si substrates and that of Si nanopillar arrays on Si substrates. The diameter of Ag nanospheres, the period of the arrays, the diameter and height of Si nanopillars have important influences on the reflection. This work provide a practicable method for the optimization of anti-reflection in different device applications.

Improving the luminous efficiency of gallium nitride-based light-emitting diodes using Ag nanograting structure

In order to improve the traditional gallium nitride (GaN)-light-emitting diode (LED) luminous efficiency, a structure of the GaN-LED is designed based on the local field enhancement of surface plasmon (SP). The principle of improving LED luminous properties using the SP features is described in detail. The factors that affect the light extraction efficiency of this LED structure are simulated with the COMSOL software. The thickness of p-GaN layer, the thickness of indium tin oxide (ITO) layer, the grating period T , the duty ratio r , as well as the shape of the interface between p-GaN and ITO are studied. The normalized radiated powers, the normalized absorbed powers, and the electric field distribution of this structure under different structure parameters have been achieved. The results show that when the thickness of p-GaN layer is 110 nm, the thickness of ITO buffer layer is 120 nm, the period T is 370 nm, the duty ratio is 0.5, and the value of D 1 / T is 0.6. The luminous intensity of LED is higher than that of the traditional LED nearly 43 times and is nearly 36 times higher than that of the Ag nanosphere structure, and SPs can be coupled with the active layer effectively to improve the luminous efficiency of LED, providing a theoretical guide for the preparation of high-performance GaN-LED chips.

Complexes Formed by Hydrophobic Interaction between Ag-Nanospheres and Adsorbents for the Detection of Methyl Salicylate VOC.

Surface-enhanced Raman spectroscopy (SERS) has been widely investigated in many applications. However, only little work has been done on using SERS for the detection of volatile organic compounds (VOCs), primarily due to the challenges associated with fabricating SERS substrates with sufficient hotspots for signal enhancement and with the surface interfacially compatible for the VOCs. This study investigated the phase transfer of Ag-nanospheres (AgNSs) from the aqueous phase to the non-aqueous phase by electrostatic interaction induced by cationic surfactants, and the feasibility of the transferred AgNSs as SERS substrates for the determination of methyl salicylate VOC. Results indicated that one of three cationic surfactants, tetraoctylammonium bromide (TOAB) dissolved in organic solvent showed successful phase transfer of the AgNSs confirmed by several characterization analyses. The complex formed by hydrophobic interaction between the transferred AgNSs and Tenax-TA adsorbent polymer was able to be utilized as a SERS substrate, and the volatile of methyl salicylate could be easily determined from SERS measurements at 4 h static volatile collection. Therefore, the proposed new techniques can be effectively employed to areas where many VOCs relevant to food and agriculture need to be analyzed.

Tandem organic solar cells containing plasmonic nanospheres and nanostars for enhancement in short circuit current density.

In this paper, we propose double junction tandem organic solar cells with PTB7:PC70BM and PDPPSDTPS:PC60BM as the polymeric active materials to cover the wide solar spectrum from 300 nm to 1150 nm. We present novel designs and finite-difference time-domain (FDTD) simulation results of plasmonic double junction tandem OSCs in which Ag nanospheres are present over the top surface of the OSC and Ag nanostars are present in the bottom subcell which substantially enhance the absorption, short circuit current density, and efficiency of the OSC as compared to the reference tandem OSCs that do not contain any nanoparticles. Different geometries of the plasmonic nanoparticles such as nanospheres and nanostars were used in the top subcell and the bottom subcell, respectively, so that the absorption in the different spectral regimes - corresponding to the bandgaps of the active layers in the two subcells (PTB7:PC70BM in the top subcell and LBG:PC60BM in the bottom subcell) - could be enhanced. The thickness of the bottom subcell active layer as well as the geometries of the plasmonic nanoparticles were optimized such that the short circuit current densities in the two subcells could be matched in the tandem OSC. An overall enhancement of 26% in the short circuit current density was achieved in a tandem OSC containing the optimized Ag nanospheres over the top surface and Ag nanostars inside the bottom subcell active layer. The presence of plasmonic nanoparticles along with the wide spectrum absorption band of the active materials in the tandem OSC leads to a typical power conversion efficiency of ∼ 15.4%, which is higher than that of a reference tandem organic solar cell (12.25%) that does not contain any nanoparticles.

Optical properties of Au–Ag nanosphere dimer: Influence of interparticle spacing

In this paper, the extinction and near-field properties of Au–Au, Ag–Ag nanosphere homo-dimer and Au–Ag nanosphere hetero-dimer were studied by using the discrete dipole approximation method. The relation between extinction and interparticle spacing was investigated under y- polarization (perpendicular to dimer axis) and z-polarization (parallel to dimer axis) incidence. The results show that the both extinction peak position and enhancement factor of electric field are sensitive to interparticle spacing when the dimer is illuminated by z-polarization incidence. For Au–Ag hetero-dimer, double same-intensity extinction peaks in visible band were found by regulating interparticle space under z-polarization incidence, and the experience forum was obtained for realizing the double same-intensity peaks.

Silver nanocubes with high SERS performance

Hot spots have been considered as a dominant role in surface enhancement Raman scattering (SERS). Here, we investigated the size and shape effect of Ag nanocubes in surface plasmon response and SERS by both experiment and theory simulation method. Silver nanocubes with abundant “hot spots” were synthesized by a polyol method and utilized as electrodes for achieving high SERS enhancement. The absorption wavelengths of the nanocubes were tunable by changing the edge lengths of the nanoparticles. Finite-difference time-domain (FDTD) simulations were employed to investigate the local E-field generation around silver (Ag) nanocubes indicating remarkable E-field enhancement at the edges and vertexes known as “hot spots”. Then, the SERS analyses demonstrated that the SERS activity of various Ag nanocubes using crystal violet (CV) as probe molecules showed a significant enhancement. The enhancement factors of SERS show strong sensitivity between the nanoparticle size and shape. Moreover, the enhancement for CV on Ag nanocubes was significantly higher than for Ag nanospheres. Therefore, the stable and high-performance of Ag nanocubes SERS system shows great application prospects in both scientific researches and practical application.

Biosynthesis of Ag nanospheres using waste phoenix dactylifera argonne: a prospective anticancer and antibacterial

In this study, we demon strate the possibility of using the aqueous extract of phoenix dactylifera (palm) argonne (argonne is a curved part in the palm holding the dates) as bio-reducing agent to prepare Ag nanoparticles. The resulting Ag nanoparticles are characterized using the following techniques: UV–vis, FTIR, XRD, EDAX, SEM and TEM. Surprisingly, the results prove that silver sizes ranged from 42 to 45 nanometers with spherical shape and the silver nanospheres also show high stability, no agglomeration for 30 days. Moreover, the ability of these nanospheres (126–7.875 μg ml−1) to inhibit E. coli bacteria was successfully tested. The antibacterial result shows that the MIC is 11.812 μg ml−1 from silver nanospheres. Moreover, the kinetic study on E. coli growth is also studied to determine the lower incubation time kills E. coli. The effect of 7.875 μg ml−1 of newly prepared Ag nanospheres on bacterial morphology is determined by the SEM technique for three different incubation times. Furthermore, the anticancer activity of the prepared nanoparticles is evaluated by MTT proliferation assay against prostate cancer cell line (in vitro) showing potent anti-tumor effect (TGI value of 8.1 μg ml−1) against PC3 cells.

Tunable Plasmon Induced Transparency in Graphene and Hyperbolic Metamaterial-Based Structure

A specially designed tunable hyperbolic metamaterial (HMM) based on plasmon induced transparency (PIT) of fractal in the near-infrared (NIR) regime was proposed. The HMM-layer constitutes the top metasurface, which is comprised of fractal-like nanospheres of silver (Ag) metal. A bilayer of graphene is sandwiched between the top HMM and bottom silicon (Si) substrate. The permittivity of graphene bilayer was deduced corresponding to different chemical potentials (of graphene). PIT of the proposed structure was obtained in the 3000-4000 nm wavelength band by employing the finite difference time domain simulation under the excitation of a fundamental transverse magnetic (TM) mode. The effects of incidence angle and graphene chemical potential on the transmission characteristics were investigated. Furthermore, the PIT windows could be tuned by altering the radii of Ag nanospheres in the HMM layer and chemical potential of bilayer graphene. Such systems would be useful in varieties of applications, e.g., switching, energy harvesting, sensing in environmental, and/or medical diagnostics, particularly in detecting the existing impurities in human blood and urine.

Multi-positional silver nanostructures for high absorption enhancement in polymer solar cells

Abstract Plasmonic effects of metal nanostructures have been widely explored to increase light absorption in polymer solar cells (PSCs). High absorption enhancement in a broad spectral range is highly desirable to boost the efficiency of PSCs. In this study, we numerically demonstrate broadband active layer absorption enhancement using plasmonic effects of multi-positional Ag nanospheres (Ag NSs). The Ag NSs were included simultaneously in two different locations, one at the top portion of active layer and the other at anode buffer layer/active layer interface. A high absorption enhancement of 66% was achieved in an 80 nm thick active layer by optimizing size and period of Ag NSs. The effect of active layer thickness on absorption enhancement has also been investigated. Large near-field enhancement around the NSs and efficient trapping of light within the active layer were found to be responsible for the high absorption enhancement.

Self-cleaning SERS membrane for reusable and ultrasensitive molecular detection via integrating graphitic‑carbon-nitride nanosheets and Ag nanospheres into hierarchical graphene layers that covered with graphitic‑carbon-nitride quantum-dots

Abstract Self-cleaning ability is an attractive parameter for fabricating practical surface enhanced Raman scattering (SERS) substrates. Thus, it is an important issue for searching suitable materials to decompose molecules inside SERS “hot spots”. Here we fabricate a flexible CNs/AgNSs@CNQDs-GLs SERS membrane for visible-light derived reusable molecular detection, via integrating graphitic‑carbon-nitride nanosheets (CNs) and Ag nanospheres (AgNSs) into graphene layers that covered with graphitic‑carbon-nitride quantum-dots (CNQDs-GLs). This membrane exhibits strong SERS activity due to the high pre-concentration ability to analytes via the delocalized π-bond, and well-rounded self-cleaning performance due to: i) the bottomed CNQDs-GLs as photocatalytic platforms degrade molecules inside nanogaps; and ii) the CNs on AgNSs@CNQDs-GLs surfaces decompose molecules outside nanogaps. This reusable membrane can be used for rhodamine B (RhB) or methylene blue (MB) fully-recovered circle-detection with a limit of 10−14 M. The practicability of this membrane is shown by detection-photodegradation cycle-runs of 4-chlorophenol, and no obvious performance loss can be observed. Thus, this membrane provides an effective route to overcome one-off substrates or incomplete self-cleaning substrates, for developing green sensing techniques.