Nanoscale Silver Research Articles

Adsorption analysis of nitrophenol isomers on silver nanostructures by surface-enhanced spectroscopy

SEIRA, SERS, TPD and DFT were used to study 4-nitrophenol (4NP), 3-nitrophenol (3NP) and 2-nitrophenol (2NP) adsorption on nanoscale silver films/powder. SERS and DFT demonstrated that 4NP adsorbed as the 4-nitrophenolate ion. SEIRA results revealed that a 4NP multilayer condensed differently using deposition solvents with and without polar bonds. 3NP and 2NP adsorption were not altered by the polar properties of the solvent. The nanoscale properties of the silver films/powder were shown to impact how the polar properties of the deposition solvent altered nitrophenol adsorption. In the SEIRA spectra of 4NP and 3NP a C O stretch was observed above 1700 cm −1 using a highly volatile n-pentane deposition solvent. No other solvent yielded such a peak for 4NP or 3NP adsorption including n-heptane. 2NP had a C O stretch regardless of deposition solvent. A C O stretch confirmed nitrophenol ionization in the monolayer and pointed toward the significance of resonance in NP adsorption. 2NP never formed a multilayer at high exposures as demonstrated using TPD and SEIRA. Results of this work will have environmental implications and will aid biochemical and industrial applications where phenolic compounds are employed.

NANOSILVER IN THE WASH

SOCKS AND OTHER GARMENTS that stay odor-free thanks to antimicrobial nanoscale silver particles are increasingly showing up on store shelves. But what happens to the silver when such products are washed remains an open question. New research by Bernd Nowack and colleagues at the Swiss Federal Laboratories for Materials Testing & Research provides a first look at the behavior of nanosilver textiles under real-world washing conditions ( Environ. Sci. Technol. , DOI: 10.1021/es9018332). The work builds on earlier studies conducted in water without detergents by researchers at Arizona State University (C&EN, April 14, 2008, page 10). Nowack and colleagues found that the total amount and form of silver (dissolved or particulate) that leaches during washing varies significantly depending on the product and the conditions. The researchers tested nine textiles and found that the percentage of total silver lost during washing varied from less than 1% to 45%. “Some particles are only loosely attached to the ...

Ion Beam Synthesis of Nanoscale Silver Clusters in a Soda-Glass Matrix

Enhanced surface segregation of Ag atoms has been experimentally observed during low dose-rate (∼0.6 A/cm2) implantation of 1 MeV silver ions (Ag+) into a soda-glass matrix at room temperature. Formation of various sizes of silver nanoclusters has further led to interesting optical properties, particularly at higher implantation doses. Drastic reduction in optical density and increase of resonance width has been explained as a result of segregated large clusters of silver atoms on the glass surface.

Intra/Extracellular Biosynthesis of Silver Nanoparticles by an Autochthonous Strain of <I>Proteus mirabilis</I> Isolated fromPhotographic Waste

There is an enormous interest in developing green synthesis procedures for production of nanoparticles by using biomimetic approaches. In our research focus has been given to the development of an efficient and eco-friendly viable process for the synthesis of nanoscale silver particles using Proteus mirabilis PTCC 1710, a bacterial strain that was isolated during a screening program from photographic waste. A significant result of this study is our observation that silver nanoparticles could be induced to synthesis intra and extracellulary. The silver nanoparticles were characterized by means of UV-Vis spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and atomic absorption spectrometer (AAS). The nanoparticles exhibited maximum absorbance at 400-410 nm in UV-Vis spectroscopy. TEM images showed formation of stable silver nanoparticles of spherical shape with most of the particles in the size range of 10-20 nm. It was found that incubation of bacterial cells in Muller-Hinton broth medium resulted in higher extracellular synthesis of silver nanoparticles, whereas intracellular synthesis of silver nanoparticles effectively increased in tryptic soy broth. The method of extraction of intracellular silver nanoparticles was inexpensive, simple and effective in large scale with no need to complex instruments. The bacteria work as a bionanofactory which continued to grow after synthesis of silver nanoparticles. The silver reduction by this strain is occurred through energy-dependent processes that lead to the high output of this reaction. Hence this new approach of using a non-pathogenic bacterial strain for the successful synthesis of nanosized silvers could be easily scaled up which establishes its commercial viability.

Applying Anand model to low-temperature sintered nanoscale silver paste chip attachment

Tensile behaviors of low-temperature sintered films of a nanoscale silver paste used for chip-attachment are studied. Stress–strain curves of partially sintered films were measured at different temperatures and strain rates on a dynamic mechanical analyzer (DMA). The tensile strength of the sintered silver films decreased with increasing temperature or with decreasing strain rate. Then the uniaxial tensile inelastic deformation behaviors of the material were simulated by a unified visco-plastic constitutive model, Anand model. Finally, finite element simulation of chip-attachment using this interface material under thermal cycling was done with Anand model via ANSYS software. The simulation results showed that accumulation of plastic strain took place in the silver-bonding layer during thermal cycling, which might lead to the final failure of the chip-attachment.

Biological Synthesis of Ag Nanoparticles through <i>In Vitro</i> Cultures of <i>Brassica Juncea</i> C. zern

In modern nanotechnology one of the most exciting area of research is the formation of nanoparticles through the biological interventions. Microbes and plants have inherent capacity to reduce metal through their specific metabolic pathway. In the present study Brassica juncea have been used to produce silver nanoparticles. Seedlings of B. juncea prepared in vitro and 14-days old plants were transferred into nutrient solution augmented with silver nitrate (25-2000 μM) allow the plants to grow in hydroponic culture for seven days. Then, the plants are harvested and analyzed through UV-VIS spectrophotometer and by Transmission Electron Microscopy (TEM) that confirms the nanoscale silver nanoparticles. We have found absorption peak in visible range (420-430 nm) of spectrum that is chiefly due to the silver nanoparticles. These biological synthesis methods considered as environmentally safe because of no toxic byproducts. Moreover, size of the nanoparticles can also be controlled by altering some conditions like pH, concentration of AgNO3 and temperature. Silver nanoparticles have large number of applications in non-linear optics, spectrally selective coating for solar energy absorption, biolabelling intercalation materials for electrical batteries, as optical receptors, catalyst in chemical reactions and as antibacterial capacities. So if these nanoparticles are synthesized by the biological methods, this would be more eco-friendly than the other common methods.

Synthesis of Nano-Scale Photocatalyic TiO2 Powder Doped withAg by Sonochemistry Reaction

In chemistry, the study of sonochemistry is concerned with understanding the effect of sonic waves and wave properties on chemical systems. In the area of chemical kinetics, it has been observed that ultrasound can greatly enhance chemical reactivity in a number of systems by as much as a million-fold. Nano-technology is a super microscopic technology in which structures of 100 nanometers or smaller can be investigated. This technology has been used to develop <TEX>$TiO_2$</TEX> materials and <TEX>$TiO_2$</TEX> devices of that size. Thus far, electrochemistry methods and photochemistry methods have generally been used to create <TEX>$TiO_2$</TEX> nano-size particles. However, these methods are complicated and create pollutants as a by-product. In the present study, nano-scale silver particles (5 nm) were prepared in a sonochemistry method. Sonochemistry deals with mechanical energy that is provided by the collapse of cavitation bubbles that form in solutions during exposure to ultrasound. <TEX>$TiO_2$</TEX> powders 25 nm in size doped with Ag were formed using an ultrasonic sound technique. The experimental results showed the high possibility of removing pollution through the action of a photocatalyst. This powder synthesis technique can be considered as an environmentally friendly powder-forming processing owing to its energy saving characteristics.

Electromechanical Behavior of Nanoscale Silver Coatings on PET Fibers

AbstractPlasma‐assisted deposition of silver films on PET mono‐ and multifilament fibers provides conductive fibers for wearable electronics. The nanoscale films were prepared in a continuously running low pressure plasma process using an ICM design for sputtering from a silver target combined with a prior RF cleaning step. The electrical resistance of the as‐deposited layers was measured in situ enabling an immediate feedback of the electrical properties, the film quality, applied Ag mass, and film thickness. The deposited quantity of Ag mass on the PET fibers was investigated by ICP‐OES and was correlated with the electrical resistance of the film. The metallized fibers showed excellent mechanical properties for wearable electronics as demonstrated by tensile properties measurement.magnified image

Tensile Behaviors and Ratcheting Effects of Partially Sintered Chip-Attachment Films of a Nanoscale Silver Paste

The mechanical behaviors of partially sintered thick films of a nanoscale silver paste used for attaching semiconductor chips are studied. The films, about 150 μm thick, were made by repeatedly stencil-printing the paste on a ceramic substrate and sintering by a recommended heating profile suitable for device attachment. The partially sintered films were lifted off the substrate, and their tensile behaviors, i.e., stress–strain curves, were measured at temperatures between −60°C and 300°C using a dynamic mechanical analyzer (DMA). The elastic modulus and tensile strength of the sintered silver films decreased with increasing temperature. Ratcheting behaviors of the films under cyclic tension at 150°C were also tested by using the DMA by examining the effects of loading rate, mean stress, and stress amplitude. The ratcheting strain grew with increasing mean stress or stress amplitude and with decreasing loading rate.

Effect of filler incorporation route on the properties of polysulfone–silver nanocomposite membranes of different porosities

Flat sheet porous polysulfone–silver nanocomposite membranes were synthesized by the wet phase inversion process. The effects of casting mixture composition and nanoparticle incorporation route on the morphological and separation properties of prepared membranes were studied by comparing nanocomposites of different preparations with silver-free controls. Silver nanoparticles were either synthesized ex situ and then added to the casting solution as an organosol or produced in the casting solution via in situ reduction of ionic silver by the polymer solvent. Nanocomposite membranes of three types differing in skin porosity and macrovoid structure were prepared. The structure and properties of nanocomposites were interpreted in terms of the coupling between the processes of nanoparticle formation and gelling of the polymer-rich phase during phase inversion. Larger nanoparticles preferentially located in the skin layer were observed in composites prepared via the ex situ method while in situ reduction of silver led to formation of smaller nanoparticles homogeneously distributed along the membrane cross-section. In some cases, incorporation of nanoscale silver formed ex situ resulted in macrovoid widening and an order of magnitude decrease in hydraulic resistance accompanied by only a moderate decrease in rejection. The accessibility of the silver nanoparticles embedded in the membrane was quantitatively assessed by the degree of the growth inhibition of a membrane biofilm due to the ionic silver released by the nanocomposites and was found to depend on the method of silver incorporation.

Microwave Freeze Drying of Sea Cucumber Coated with Nanoscale Silver

To develop an improved dehydration method for sea cucumber, microwave freeze drying was tested as a potential method. According to our experimental results, microwave freeze drying can reduce drying time to about half of the traditional vacuum freeze-drying process. To ensure a high degree of sterilization, a novel nanoscale silver coating technique was combined with microwave freeze drying. Microwave freeze drying combined with nanoscale silver coating treatment leads to a much lower microorganism number with no significant effect on drying efficiency and sensory quality.

Interaction of DNA bases with silver nanoparticles: Assembly quantified through SPRS and SERS

Colloidal silver nanoparticles were prepared by reducing silver nitrate with sodium borohydride. The synthesized silver particles show an intense surface plasmon band in the visible region. The work reported here describes the interaction between nanoscale silver particles and various DNA bases (adenine, guanine, cytosine, and thymine), which are used as molecular linkers because of their biological significance. In colloidal solutions, the color of silver nanoparticles may range from red to purple to orange to blue, depending on the degree of aggregation as well as the orientation of the individual particles within the aggregates. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and absorption spectroscopy were used to characterize the assemblies. DNA base-induced differential silver nanoparticle aggregation was quantified from the peak separation (relates to color) of surface plasmon resonance spectroscopy (SPRS) and the signal intensity of surface-enhanced Raman scattering (SERS), which rationalize the extent of silver–nucleobase interactions.

Preparation and Characterization of Silver Citrate Nano-Emulsion and Nano-Silver Film

To prepare the nano-scale silver carboxylate emulsions and investigate their applications in the preparation of nano-scale silver films, the silver citrate emulsion was synthesized through the reaction of silver nitrate with sodium citrate in the presence of polyvinylpyrrolidone (PVP) as a surface modification agent in water. The emulsion was coated onto the surface of the PET substrate to form a thin latex layer of silver citrate. And this was followed by drying at about 100 °C. Then, the silver citrate thin film was deoxidized by aqueous ascorbic acid. Finally, a translucent silver thin film was formed on the surface of the PET substrate. Properties of the silver citrate emulsion and the silver film on the PET were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), laser particle size analysis, scanning electron microscopy (SEM), thermogravimetry(TG) ,UV-visible absorption spectroscopy, atomic force microscopy(AFM) and digital multimeter analysis. It was found that the silver citrate particle surface-modified by PVP has a nano-rod structure and homogeneous size distribution. The nano-rod was about 20 nm in diameter and 200 nm in length. For the UV-visible absorption spectrum of the thin film exhibited an absorption peak at 430 nm, the silver thin film prepared on the surface of the PET substrate was a typical nano-scale sliver film. Measurements of the sliver thin film at room temperature indicated that the silver film was electrically conductive, and the surface resistance was 2.42 k5/cm.

Sacrificial passivation of nanoscale silver particles

Solid-state reaction in particle compacts comprising organically capped nanoscale Ag particles and Sn was evaluated. The results indicate that all of the Sn initially present formed a liquid phase when combined with sodium dodecyl sulfate (SDS)-capped particles, while smaller fractions were obtained when combined with polyvinylpyrrolidone- and poly(vinyl alcohol) (PVA)-capped nanoscale and uncapped micron-sized Ag. The extent of the subsequent liquid phase reaction is demonstrated not to be adversely affected by the presence of the SDS and PVA caps.

Negative and linear positive magnetoresistance effect in silver-rich silver selenide

In the non-magnetic semiconductor silver selenide (Ag 2+ δ Se) with a minor heterogeneous silver excess (0.79 × 10 −4 < δ ≤ 1 × 10 −2) we measured either a saturating negative magnetoresistance (MR) effect, a linear positive MR effect or a superposition of both. This complex MR behavior depends on the amount of the silver metal excess, but is also strongly influenced by the thermal treatment of the samples. Excess silver that cannot be accommodated homogeneously in the silver selenide lattice creates structural heterogeneities and forms a microstructure which is controlled by the thermal annealing procedure. We suggest that small silver segregations at the grain boundaries of the silver selenide matrix (“nanofilms”) are responsible for the negative MR effect, whereas nanoscale silver particles within the silver selenide matrix (nanoparticles) cause a linear positive effect.

Finite-Difference Time-Domain Study of Guided Modes in Nano-Plasmonic Waveguides

A conformal dispersive finite-difference time-domain (FDTD) method is developed for the study of one-dimensional (1-D) plasmonic waveguides formed by an array of periodic infinite-long silver cylinders at optical frequencies. The curved surfaces of circular and elliptical inclusions are modelled in orthogonal FDTD grid using effective permittivities (EPs) and the material frequency dispersion is taken into account using an auxiliary differential equation (ADE) method. The proposed FDTD method does not introduce numerical instability but it requires a fourth-order discretisation procedure. To the authors' knowledge, it is the first time that the modelling of curved structures using a conformal scheme is combined with the dispersive FDTD method. The dispersion diagrams obtained using EPs and staircase approximations are compared with those from the frequency domain embedding method. It is shown that the dispersion diagram can be modified by adding additional elements or changing geometry of inclusions. Numerical simulations of plasmonic waveguides formed by seven elements show that row(s) of silver nanoscale cylinders can guide the propagation of light due to the coupling of surface plasmons.

Low-Temperature Sintering of Nanoscale Silver Paste for Large-Area Joints in Power Electronics Modules

Today, reflow soldering is a commonly used technique to establish large-area joints in power electronics modules. These joints are needed to attach large-area (&gt;1 cm2) power semiconductor chips to the substrate, e.g., a direct-bond copper substrate, and the multichip module substrate to a copper base plate for heat spreading. Thermal performance, specifically thermal conductivity and thermomechanical reliability, of these large-area joints are critical to the electrical performance and lifetime of the power modules. Soft solder alloys, including the lead-tin eutectic and lead-free alternatives, have low thermal conductivities and are highly susceptible to fatigue failure. As demands mount for higher power density, higher junction temperature, and longer lifetime out of the power modules, reliance on solder-based joining is becoming a barrier for further advancement in power electronics systems. Recently, we successfully demonstrated lowtemperature sintering of nanoscale silver paste as a lead-free solution for achieving highperformance, high-reliability, and high-temperature interconnection of small devices (&lt;0.09 cm2). In this paper, we report the results of our study to extend the low-temperature sintering technique to large-area joints. The study involved redesigning the organic and inorganic components of the nanoscale silver paste, analyzing the burnout kinetics of the various organic species sandwiched between large-area plates, and developing desirable temperature-time profile to improve sintering and bonding strength of the joints.

High-Temperature Operation of SiC Power Devices by Low-Temperature Sintered Silver Die-Attachment

In this paper, we present the realization of high-temperature operation of SiC power semiconductor devices by low-temperature sintering of nanoscale silver paste as a novel die-attachment solution. The silver paste was prepared by mixing nanoscale silver particles with carefully selected organic components which can burn out within the low-temperature firing range. SiC Schottky diodes were placed onto stencil-printed layers of the nanoscale silver paste on Au or Ag metallized direct bonded copper (DBC) substrates for the die-attachment. After heating up to 300degC and dwell for 40 min in air to burn out the organic components in the paste and to sinter the nanoscale silver, the paste consolidated into a strong and uniform die-attach bonding layer with purity >99% and density >80%. Then the die-attached SiC devices were cooled down to room temperature and their top terminals were wire-bonded to achieve the high-temperature power packages. Then the power packages were heated up from room temperature to 300degC for high-temperature operation and characterization. Results of the measurement demonstrate the low-temperature silver sintering as an effective die-attach method for high-temperature electronic packaging. An advanced packaging structure for future SiC transistors with several potential advantages was also proposed based on the low-temperature sintering technology.

Optical properties of silver composite metamaterials

We present a computational and experimental study investigating the optical properties of nanoscale silver composite metamaterials fabricated by ion beam lithography. Both simulations and experimental results demonstrate high transmission efficiencies in the near infra-red through these devices. Implications for experimentally verifying the calculated near-field distributions of these materials are also discussed.

New synthetic approach produces mondisperse palladium nanoparticles

Nanoscale metallic nanoparticles in the 1–4nm size regime are of great interest due to their electronic, catalytic, and, in some cases, optical properties. For example, within this size range, electronic properties transition from a bulk-like continuum of electronic states to molecule-like, discrete electronic orbital levels.1 Gold and silver nanoscale particles have been studiedmore than other metals largely due to their ability to absorb and scatter light in the visible region of the electromagnetic spectrum. They are also more stable toward oxidation as compared with other metals. Only a few reports demonstrate the voltammetry or electrochemical properties of other metal nanoparticles in the 1–4nm size regime.2 Our group has developed synthetic strategies that produce monodisperse metal nanoparticles with diameters less than 4nm. We have also studied the charge transfer properties of these nanoparticles. Gram-scale production of well-defined, monodisperse 1–4nm metal particles is a major challenge. We have been particularly successful with palladium (Pd) nanoparticles, which we have intensively pursued since Pd is often used as a catalyst in organic transformations. Examples include carbon-carbon coupling reactions and olefin hydrogenation reactions. The high surfaceto-volume ratio and increase in surface atom distribution of the nanoparticles greatly enhance the metal’s catalytic activity. Several procedures that produce Pd nanoparticles have been reported, but only a few of these yield monodisperse nanoparticles in the 1–4nm size regime. Typical stabilizing ligands for Pd nanoparticles include dendrimers3 and thiols.4, 5 Ourmethod makes use of thioethers with dual functions as both stabilizing and reducing agents. Figure 1 shows Pd nanoparticles of 1.7 ± 0.2 and 3.5 ± 0.1nm that were synthesized with n-dodecyl sulFigure 1. Transmission electron microscopy images of palladium (Pd) nanoparticles synthesized in our laboratory: (a) 3.5± 0.1nm, and (b) 1.7± 0.2nm in diameter. Scale bar = 50nm. The insets show corresponding size distributions obtained by counting 100 randomly selected particles.