Synthesis and formation mechanism of Ag–Ni alloy nanoparticles at room temperature

Ag–Ni nanoparticles were prepared with a chemical reduction method in the presence of polyvinylpyrrolidone (PVP) used as a stabilizing agent. During the synthesis of Ag–Ni nanoparticles, silver nitrate was used as the Ag⁺ source while nickel sulfate hexahydrate was used as Ni²⁺ source. Mixed solutions of Ag⁺ source and Ni²⁺ source were used as the precursors and sodium borohydride was used as the reducing agent. Five ratios of Ag⁺/Ni²⁺ (9:1, 3:1, 1:1, 1:3, and 1:9) suspensions were prepared in the corresponding precursors. Ag–Ni alloy nanoparticles were obtained with this method at room temperature. Scanning electronic microscope (SEM), energy dispersive spectrum (EDS), high resolution transmission electron microscope (HRTEM) were used to characterize the morphology, composition and crystal structure of the nanoparticles. The crystal structure was also investigated with X-ray diffraction (XRD). In all five Ag/Ni ratios, two kinds of particle structures were observed that are single crystal structure and five-fold twinned structure respectively. Free energy of nanoparticles with different crystal structures were calculated at each Ag/Ni ratio. Calculated results revealed that, with identical volume, free energy of single crystal particle is lower than multi-twinned particle and the difference becomes smaller with the increase of particle size; increase of Ni content will lead the increase of free energy for both structures. Formation of different crystal structures are decided by the structure of the original nuclei at the very early stage of the reduction process.     

Nonlinear optical properties of nanometer-size silver composite azobenzene containing polydiacetylene film

Diacetylene monomer containing p-nitrophenyl azobenzene moiety (NADA) was synthesized. Silver nanoparticles with different concentrations were adulterated in the above polymerized NADA (PNADA) films and the third-order nonlinear optical properties were investigated in detail. UV–vis spectra and transmission electron microscopy were used to confirm the formation of PNADA/Ag nanocomposite films. The silver nanoparticles (average size of 10 nm) were well dispersed in the polymer films. The value of the nonlinear refractive index n ₂ for PNADA films (8.48×10⁻¹⁵ cm²/W) was much higher than that of pure polydiacetylene films. Further, the introduction of silver nanoparticles into the PNADA polymer films led to the further enhancement of nonlinear optical properties. The maximum value of n ₂ for PNADA/Ag nanocomposite films could be 11.6×10⁻¹⁵ cm²/W. This enhancement should be ascribed to the surface plasmon resonance of silver nanoparticles.     

Synthesis of silver nanocomposites by SCF impregnation of matrices of synthetic opal and Vycor glass by the Ag(hfac)COD precursor

Silver-containing nanocomposites were prepared by impregnating Vycor glass (a pore diameter of 4 nm) and synthesized opal matrices (an interstitial void size of 40 nm) with cyclooctadiene complex of silver hexafluoroacetylacetonate (Ag(hfac)COD), a silver precursor, dissolved in supercritical carbon dioxide and were examined by optical absorption spectroscopy, atomic force microscopy, and electron spin-resonance spectroscopy. It was demonstrated that the absorption spectra of Vycor glass and opal matrices impregnated with Ag(hfac)COD molecules and subjected to thermal treatment in air at temperatures above 50°C exhibit plasmon resonances characteristic of Ag nanoparticles at 420–430 nm. The peculiarities of the plasmon resonance band for both types of samples were attributed to the morphology of the pore space in which silver particles are formed. Paramagnetic Cu(hfac)₂ molecules (copper hexafluoroacetylacetonate) were used as a spectroscopic probe for estimating the distribution of the precursor in the pores of Vycor glass and opal matrices during supercritical fluid impregnation.     

Luminescence of CdS:Ag Quantum Dots in a Polymethacrylate Matrix

Semiconductor quantum dots (QDs) exhibit intense luminescence and reproduce optical characteristics. Doping with metal ions has a positive effect on their properties. Introduction of QDs into polymer matrices leads to the formation of a required morphology of composites. There is a problem in synthesis of optically transparent polymer composites containing QDs of the А²В⁶ group that consists in the extremely low solubility of metal chalcogenides and most of their precursors in monomers. To solve this problem, we used colloidal synthesis. CdS QDs were synthesized by the method of appearing reagents in situ in methylmethacrylate (MMA). Doping with Ag⁺ ions was performed by adding a silver salt into the reaction mixture during the synthesis of CdS QDs. The PMMA/CdS:Ag luminescent polymer glasses were synthesized by radical block polymerization of MMA. The transparency of the composites at wavelengths exceeding 500 nm reaches 92% (5 mm). The luminescence excitation is related to the interband electron transitions in CdS crystals. Luminescence in the range of 500–600 nm is observed due to electron relaxation via a system of levels in the band gap of doped CdS crystals. The positions and intensities of the spectral bands depend on the Ag⁺ concentration, particle size, excitation wavelength, and other factors. The formation of Cd(Ag)S/Ag₂S structures at Ag⁺ concentrations higher than 5.0 × 10^–3 mol/L quenches the luminescence.     

Formation of argentic clusters and small Ag nanoparticles in soda-lime silicate glass

The formation of argentic clusters and very small Ag nanoparticles of 0.5 to 2 nm size in commercial soda-lime glass silver-doped by Ag/Na ion exchange in a mixed nitrate melt has been studied by electron microscopy and EXAFS. Particles formation was induced already during the ion exchange procedure, or by subsequent ion irradiation with 1.5 MeV He⁺ or 3 MeV Au⁺. The presence of nanoparticles was also macroscopically revealed by their surface plasmon resonance. The structural characterization indicates that specific configurations of silver oxide-like structures, so-called argentic clusters, are involved in the initial stage of nanoparticles formation.     

Plasmon-enhanced luminescence of Sm complex using silver nanoparticles in Polyvinyl Alcohol

Silver (Ag) nanoparticles (NPs) were prepared by laser ablation in water with an aim to enhance the luminescence of rare earth coordinated complex in polymer host. A fixed concentration of the complex containing Samarium (Sm), Salicylic acid (Sal) and 1, 10-phenanthroline (Phen) were combined with different concentrations of silver NPs in PolyVinyl Alcohol at room temperature. Absorption spectrum and XRD patterns of the sample show that the Sm(Sal)₃Phen complex is accompanied by Ag NPs. The luminescence from the complex was recorded in the presence and absence of Ag NPs using two different excitation wavelengths viz. 400 and 355 nm. Of these, 400 nm radiation falls in the surface plasmon resonance of Ag NPs. It was found that the Ag NPs led to a significant enhancement in luminescence of the complex. Surprisingly, a high concentration of Ag NPs tends to quench the luminescence.     

Silver nanoparticles produced by PLD in vacuum: role of the laser wavelength used

In this work we report the results of investigation of silver (Ag) nanoparticles prepared on a silica substrate by laser ablation. Our attention was focused on the mean diameter, size distribution and optical absorption properties of nanoparticles prepared in vacuum by using different laser wavelengths. The fundamental wavelength and the second, third, and fourth harmonics of a nanosecond Nd:YAG laser were used for nanoparticles fabrication. The corresponding values of the laser fluence for each wavelength were: 0.6 J/cm² at 266 nm, 0.8 J/cm² at 355 nm, 2.8 J/cm² at 532 nm, and 2 J/cm² at 1064 nm. The Ag nanoparticles produced have mean diameters in the range from 2 nm to 12 nm as the nanoparticles’ size decreases with the decrease of the wavelength used. The presence of the Ag nanoparticles was also evidenced by the appearance of a strong optical absorption band in the measured UV-VIS spectra associated with surface plasmon resonance (SPR). A redshift and widening of the absorption peak were observed as the laser wavelength was increased. Some additional investigations were performed in order to clarify the structure of the Ag nanoparticles.     

Photo–induced processes in Ag and Eu β-diketonates incorporated into aerogel matrix of silicon dioxide by supercritical fluid impregnation

Samples of silicon dioxide aerogel with embedded Ag and Eu β-diketonate molecules are obtained by impregnation in supercritical carbon dioxide (SC-CO₂). The sample impregnated by Eu(tta)₃ molecules possesses photoluminescence properties. Moreover, adsorption of Eu(tta)₃ on the walls of the pores results in a strong broadening of the Stark components of its photoluminescence spectra. It is found that aerogel impregnation by AgFOD molecules followed by laser irradiation causes the formation of Ag nanoparticles in the sample volume as a result of AgFOD photolysis and subsequent diffusion self-assembly. The Ag nanoparticles assemble into filament structures due to self-organization as they focus laser radiation.     

Non-linear optical properties of silver nanoparticles prepared by hydrogen reduction method

Silver nanoparticles have been prepared using hydrogen gas as the reducing agent for silver nitrate and poly(vinyl pyrrolidone) as the capping agent; the reaction was carried out at 70 °C for 3 h. The size of the nanoparticles was found to be about 20 nm as analyzed using transmission electron micrographs. The X-ray diffraction pattern revealed the face-centered cubic (fcc) structure of silver nanoparticles. The linear absorption of Ag nanoparticles, α, is obtained about 3.71 cm⁻¹. The non-linear refractive indices of silver nanoparticles were defined by the z-scan technique using CW He-Ne laser (λ = 632.8 nm) at different incident intensities. The magnitude of non-linear refractive index (n₂) was measured to be in the order of 10⁻⁷ (cm²/W) with a negative sign. Therefore self-defocusing phenomena is taking placed for Ag nanoparticles.     

Dynamics of formation and decay of supercritical fluid silver colloid under pulse laser ablation conditions

The effect of the density of supercritical carbon dioxide (SC-CO₂) on the dynamics of formation of supercritical fluid (SCF) silver colloids during pulse laser ablation and their post-pulse degradation was studied by in situ UV/vis absorption spectroscopy. Laser irradiation of a silver target in SC-CO₂ caused ablative formation of Ag nanoparticles of different shapes and sizes: quasi-spherical particles (~4 nm) and larger Ag nanoparticles (hundreds of nanometers). A change in the colloid density from 0.24 to 0.82 g/cm³ caused significant changes in the dynamics of ablative formation of large and small particles, the rate of aggregation of small Ag particles into large particles, and the rate of gravitation-induced sedimentation of nanoparticles in the SCF colloid.     

掺杂Ag纳米粒子对偶氮聚合物光致异构效应的影响

报道了通过宏观测量偶氮聚合物光致异构效应,及其引起的光学各向异性变化,讨论了一种影响偶氮聚合物顺反异构效应的有效途径。在偶氮高分子聚合物中,添加了不同浓度的Ag纳米粒子,采用了波长为442nm的He-Cd偏振激光为激发光源,当Ag纳米粒子掺杂质量浓度为0.12μg/ml的时候,激发了薄膜样品中Ag纳米粒子的等离子体共振效应,增强了粒子周围纳米尺度的电磁场强度,相当程度上提高了偶氮聚合物光致异构的转换效率;另外,研究了不同的取代基同纳米Ag粒子的相互作用对光致异构效应的影响,探讨了一种能够有效地控制光致异构效应的方法。     

Comparison of silver nanoparticles confined in nanoporous silica prepared by chemical synthesis and by ultra-short pulsed laser ablation in liquid

Hexagonally ordered mesoporous silica materials, MCM-41 and SBA-15, have been synthesized and loaded with Ag nanoparticles, utilizing both chemical synthesis and ultra-short pulsed laser ablation in liquid. In laser ablation, a silver target, immersed in aqueous suspension of ordered mesoporous silica SBA-15, was irradiated by ultra-short laser pulses to generate silver nanoparticles. For comparison, samples of similar silver contents were prepared either by incorporating silver into the SBA-15 during a hydrothermal synthesis or by introducing silver in MCM-41 by template ion-exchange. Samples were characterized by XRD, N₂ physisorption, TEM and UV–vis spectroscopy. All preparations contained significant amount of 5–50 nm size silver agglomerates on the outer surface of the silica particles. The laser ablation process did not cause significant destruction of the SBA-15 structure and metallic silver (Ag⁰) nanoparticles were mainly generated. It is demonstrated that by laser ablation in aqueous silica suspension smaller and more uniform metallic silver particles can be produced and loaded on the surface of the silica support than by synthesis procedures. Catalytic properties of the samples have been tested in the total oxidation of toluene. Because of its favorable Ag dispersity, the Ag/SBA-15 catalyst, generated by the laser ablation method, had better catalytic stability and, relative to its Ag load, higher activity than the conventional Ag/SBA-15 preparations.     

Synthesis of PMA stabilized silver nanoparticles by chemical reduction process under a two-step UV irradiation

Poly(methacrylic acid) (PMA) stabilized silver nanoparticles (Ag NPs), also used in the surface modification of clothing fibers, were fabricated via chemical reduction processes under UV irradiation. To obtain an uniform size distribution it has been designed a new “two-step” process which employs two different UV radiation densities in order to control the kinetics of NPs nucleation. The as produced nanoparticles were characterized by UV-vis absorption spectroscopy and TEM microscopy. The results show the reduction of the Ag ions and the nanoparticles nucleation in the first step. In the second step, the final Ag NPs size distribution is controlled through a quick cross-linking of the PMA that freezes out any further modification. A narrow size distribution with more than 80% NPs smaller than 10 nm and none larger than 25 nm was obtained and the long-term stability (one month) of the colloidal solution was verified.     

Laser induced microrelief superstructure of Ag/ITO seed-mediated nanocomposites

The topography of indium tin oxide (ITO) films with incorporated silver nanoparticles and irradiated by single pulses of 18 ns Nd:YAG laser has been investigated. The study was carried out with two Ag/ITO films having resistances of 50 Ω/ITO sheet and 4 Ω/ITO sheet. The periodic structures in both samples were created after the laser treatment. The photo-induced periodic structures have a different character while the sheet resistance plays a major role in the growth process of these structures. The results of optical and non-linear optical investigations lead us to the conclusion that the temporary polarization of samples during laser treatment is responsible for the shape of periodic structures.     

Synthesis and photo physical properties of Au @ Ag (core @ shell) nanoparticles disperse in poly vinyl alcohol matrix

Synthesis of core @ shell (Au @ Ag) nanoparticle with varying silver composition has been carried out in aqueous poly vinyl alcohol (PVA) matrix. Core gold nanoparticle (~15 nm) has been synthesized through seed-mediated growth process. Synthesis of silver shell with increasing thickness (~1–5 nm) has been done by reducing Ag⁺ over the gold sol in the presence of mild reducing ascorbic acid. Characterization of Au @ Ag nanoparticles has been done by UV–Vis, High resolution transmission electron microscope (HRTEM) and energy dispersive X-ray (EDX) spectroscopic study. The blue shift of surface plasmon resonance (SPR) band with increasing mole fraction of silver has been interpreted due to dampening of core, i.e. Au SPR by Ag. The dependence of nonlinear optical response of spherical core @ shell nanoparticles has been investigated as a function of relative composition of each metal. Simulation of SPR extinction spectra based on quasi-static theory is done. A comparison of our experimental and the simulated extinction spectra using quasi-static theory of nanoshell suggests that our synthesized bimetallic particles have core @ shell structure rather than bimetallic alloy particles.     

Corrosion processes of triangular silver nanoparticles compared to bulk silver

Excessive corrosion of silver nanoparticles is a significant impediment to their use in a variety of potential applications in the biosensing, plasmonic and antimicrobial fields. Here we examine the environmental degradation of triangular silver nanoparticles (AgNP) in laboratory air. In the early stages of corrosion, transmission electron microscopy shows that dissolution of the single-crystal, triangular, AgNP (side lengths 50–120 nm) is observed with the accompanying formation of smaller, polycrystalline Ag particles nearby. The new particles are then observed to corrode to Ag₂S and after 21 days nearly full corrosion has occurred, but some with minor Ag inclusions remaining. In contrast, a bulk Ag sheet, studied in cross section, showed an adherent corrosion layer of only around 20–50 nm in thickness after over a decade of being exposed to ambient air. The results have implications for antibacterial properties and ecotoxicology of AgNP during corrosion as the dissolution and reformation of Ag particles during corrosion will likely be accompanied by the release of Ag⁺ ions.     

Dynamic templating role of polynaphtalene sulphonate in the formation of silver nanocrystals in aqueous solution

We have used time resolved small angle X-ray scattering (SAXS) for investigating the early stages of the formation of crystalline colloidal Ag particles by AgNO₃ reduction with ascorbic acid in an aqueous acidic solution of a polynaphthalene sulphonate polymer (Daxad). In order to exploit the polymer role in silver crystallization, the measurements have been performed at different polymer concentrations. Data analysis suggests that the nucleation and growth of primary particles of about 20 nm in diameter, occurring in a surface-fractal arrangement of the dynamic polymeric template, is assisted by the development of long range spatial correlations. These correlations could be a sign of polymer-induced liquid fluctuations as intermediate precursors of Ag crystallization.     

Influence of Silver and Gold Nanoparticles and Thin Layers on Charge Carrier Generation in InGaN/GaN Multiple Quantum Well Structures and Crystalline Zinc Oxide Films

It has been shown that Ag and Au nanoparticles and thin layers influence charge carrier generation in InGaN/GaN multiple quantum well structures and crystalline ZnO films owing to the surface morphology heterogeneity of the semiconductors. When nanoparticles 10 < d < 20 nm in size are applied on InGaN/GaN multiple quantum well structures with surface morphology less nonuniform than that of ZnO films, the radiation intensity has turned out to grow considerably because of a plasmon resonance with the participation of localized plasmons. The application of Ag or Au layers on the surface of the structures strongly attenuates the radiation. When Ag and Au nanoparticles are applied on crystalline ZnO films obtained by rf magnetron sputtering, the radiation intensity in the short-wavelength part of the spectrum increases insignificantly because of their highly heterogeneous surface morphology.     

Fabrication of surface‐enhanced Raman scattering‐active ZnO/Ag composite microspheres

We show in this paper how zinc oxide (ZnO)/silver (Ag) composite microspheres can be prepared by the reduction of Ag(NH₃)₂⁺ with the reducing agent formaldehyde in aqueous solution on the surface of ZnO microspheres. During the preparation, Sn²⁺ was absorbed on the surface of ZnO microspheres for sensitization and activation, and then Ag(NH₃)₂⁺ was reduced to Ag nanoparticles by the reducing agent to obtain ZnO/Ag composite microspheres. SEM and TEM images revealed silver nanoparticles with a diameter ranging from tens to 100 nm. X‐Ray photoelectron spectra (XPS), X‐ray diffraction (XRD) patterns and UV‐vis spectra were used to characterize the structure of the ZnO/Ag composite microspheres. The origin of the surface‐enhanced Raman scattering properties was traced to the surface of the ZnO/Ag composite microspheres. The enhancement factor was estimated in detail, and the enhancement mechanism for the SERS effect was also investigated. Copyright © 2007 John Wiley & Sons, Ltd.     

Structural and spectroscopic studies of thin film of silver nanoparticles

We report the deposition of thin film of silver (Ag) nanoparticles by wet chemical method. The as-synthesized Ag nanoparticles have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray energy dispersive spectroscopy (EDS), field emission transmission electron microscopy (FETEM) and high-resolution TEM (HRTEM), UV-vis spectroscopy and thermogravimetric-differential thermal analysis (TG-DTA) respectively. FESEM image indicates that the silver film prepared on the quartz substrate is smooth and dense. XRD pattern reveals the face-centered cubic (fcc) structure of silver nanoparticles. EDS spectrum indicates that samples are nearly stoichiometric. From TEM analysis, it is found that the size of high purity Ag nanoparticles is ranging from 10 to 20 nm with slight agglomeration. Absorption in UV-vis region by these nanoparticles is characterized by the features reported in the literature, namely, a possible Plasmon peak at ∼403 nm. Optical absorbance spectra analysis reveals that the Ag film has an indirect band structure with bandgap energy 3.88 eV. TGA/DTA studies revealed that a considerable weight loss occurs between 175 and 275 °C; and the reaction is exothermic.