Volume Fraction Of Silver Research Articles

Fabrication and optical properties of chitosan/Ag nanoparticles thin film composites

Abstract Chitosan thin films with controlled thickness have been fabricated by spin-coating chitosan acetate and citrate solutions for application as planar optical waveguides (POW). “In situ” reduction of preadsorbed in chitosan film Ag + ions with sodium borohydride resulted in formation of chitosan/Ag composites, in which silver nanoparticles of a size below 10 nm were homogeneously distributed. In contrast to chitosan/Ag composites formed in solution, UV–vis spectra of the thin film composites have depicted a single narrow adsorption band at 412–413 nm independently of the silver content. The absence of long-wavelength shoulders in the spectra, which are associated with oscillations of non-spherical particles or plasmon coupling of aggregates, has confirmed SEM data on high uniformity of the Ag/chitosan composite films. We have shown that the refractive index of the composites at a wavelength of a HeNe laser (633 nm) increases from 1.53 to 1.69 with the increase of the silver volume fraction up to 2.55%. Investigations of composites waveguiding properties revealed that the light propagation is feasible up to a silver volume fraction of 1.3%, which corresponds to the maximum refractive index 1.58.

Heterogeneously structured conductive carbon fiber composites by using multi-scale silver particles

This paper reports a new approach to enhance the through-thickness thermal conductivity of laminated carbon fabric reinforced composites by using nanoscale and microscale silver particles in combination to create heterogeneously structured continuous through-thickness thermal conducting paths. High conductivity of 6.62W/(mK) with a 5.1v% silver volume fraction can be achieved by incorporating these nanoscale and microscale silver particles in EWC-300X/Epon862 composite. Silver flakes were distributed within the inter-tow area, while nanoscale silver particles penetrated into the fiber tows. The combination of different sizes of silver fillers is able to effectively form continuous through-thickness conduction paths penetrating fiber tows and bridging the large inter-tow resin rich areas. Positive hybrid effects to thermal conductivity were found in IM7/EWC300X/sliver particle hybrid composites. In addition, microscale fillers in resin rich areas showed less impact on tensile performance than nanoscale particles applied directly on fiber surface.

In situ X-ray diffraction study of the growth of silver nanoparticles embedded in silica film by ion irradiation: The effect of volume fraction

The effect of volume fraction of silver (Ag) on the growth of silver nanoparticles (AgNPs) embedded in ion-irradiated silica films is reported. Films with low volume fraction (LVF) and high volume fraction (HVF) of Ag in silica matrix were prepared by magnetron co-sputtering. The growth of AgNPs under 120MeV Ag ion irradiation is monitored in situ using grazing incidence X-ray diffraction (GIXRD). It is observed that the film with LVF shows the growth of AgNPs in a nearly single ion impact region, while the film with HVF shows a monotonous growth even in the region of multiple ion impacts. Rutherford backscattering spectrometry (RBS) experiments are also performed to determine the exact volume fraction of Ag in the silica matrix and to understand the role of sputtering and diffusion processes on the growth of AgNPs. Surface plasmon resonance (SPR) is carried out to obtain further evidence of the mechanisms of growth. Our study reveals that the growth of embedded nanoparticles strongly depends on the volume fraction of metal in the matrices and affects the dipolar interactions among such noble metal NPs.

Volume fraction dependence of transient absorption signal and nonlinearities in metal nanocolloids

Electron–lattice thermalization dynamics in metal nanoparticles or in bulk metal is usually estimated by measuring the decay time of the change in transmission following an optical excitation. Such measurements can be performed in transient absorption geometry using a femtosecond laser. We find that for silver nanoplatelet/water colloids, the decay time of the transient absorption depends on the volume fraction of silver in water. By estimating the volume fraction dependence of nonlinearities in the same samples, we show that the variation in the measured decay time is due to pump-depletion effects present in the sample. The correct correction factor for taking into account pump-depletion effects in fifth- and higher-order nonlinearities is also presented.

Photolithographic processing of silver loaded dielectric coatings based on preformed colloidal TiO2 nanoparticles dispersed in a mesoporous silica binder

Titanium dioxide is a well known photocatalyst for reactions involving surface trapped photogenerated carriers. Noble metal photo-reduction may be used for the processing of silver/TiO2 nanocomposite coatings that may exhibit interesting optical and electrical properties. We present here results of our investigations performed on an original system consisting of preformed colloidal TiO2 nanoparticles homogeneously dispersed within a mesoporous silica host matrix. Light irradiation of samples immerged in an aqueous silver salt solution leads to the homogeneous deposition of silver islands in the vicinity of the TiO2 particles and throughout the film thickness. The silver volume fraction is directly controlled by the irradiation dose up to a value of about 16 vol.%. Films exhibit tunable plasmonic properties that correspond to silver nanoparticles in interaction, and a percolation threshold is observed at 8–10 vol.%, leading to films with a conductivity of about 40 S cm−1. The major interest of this method lies in the high silver reduction quantum efficiency (about 50%) and the possibility to modulate optical and electronic properties by light irradiation while the low temperature of processing permits the photolithographic deposition of metallic patterns on organic flexible substrates.

Diffusion and conductivity of mixed-conducting Ag/CGO composites

Dense (> 95%) interpenetrating phase composites of silver and gadolinium-doped ceria (CGO) were prepared by silver plus copper oxide (Ag-6 mol% CuO) liquid metal infiltration of porous CGO pre-forms. The composites showed high relative density (above 95%), negligible gas leakage and high electronic conductivity when the volume fraction of silver was approximately 14 vol.% or greater. Oxygen isotopic exchange and depth profiling by secondary ion mass spectrometry was used to determine the oxygen tracer diffusion ( D*) and surface exchange coefficient ( k*) of the composites. Composites with 14 vol.% silver exhibited similar solid state oxygen diffusivity and thermal expansion to CGO, combined with much faster surface exchange kinetics. These results indicate that such composites are promising for further development as passive oxygen separation membranes.

A mechanism for enhanced photocatalytic activity of nano-size silver particle modified titanium dioxide thin films

Ag-TiO2 nanostructured thin films with silver volume fraction of 0–20% were deposited on silicon and quartz substrates by RF magnetron sputtering and annealed in ambient air at 950°C for 1 h. The phase structure and surface topography of the films were characterized by X-ray diffractometer and transmission electron microscope. Photocatalytic activity of the films was evaluated by light induced degradation of methyl orange (C14H14N3NaO3S) solution using a high pressure mercury lamp as lamp-house. The relation of photocatalytic activity and silver content was studied in detail. It was found that silver content influences phase structure of TiO2 thin films, and silver in the films is metallic Ag (Ag0). With increasing silver content from 0 to 20 vol%, photocatalytic activity of the films increases first and then decreases. A suitable amount (2.5–5 vol%) silver addition can significantly enhance the photocatalytic activity of TiO2 films. The enhanced photocatalytic activity was mainly attributed to the extension of visible light absorption region of the films, the presence of anatase phase, the increase of oxygen anion radicals O2− and reactive center of surface Ti3+, and the better separation between electrons and holes on the films surface.

Pure and silver (2.5–40 vol%) modified TiO 2 thin films deposited by radio frequency magnetron sputtering at room temperature: Surface topography, energy gap and photo-induced hydrophilicity

Ag–TiO 2 nanostructured thin films with silver volume fraction of 0–40% were deposited on silicon and quartz substrates by radio frequency (RF) magnetron sputtering. The phase structure, surface composition, surface topography, optical properties, and hydrophilicity of the films were characterized by X-ray diffractometer, X-ray photoelectron energy spectrometer, atomic force microscope, ultraviolet–visible spectrophotometer, and water contact angle apparatus. The relation of hydrophilic property and silver content was studied in detail. It was found that silver content influences microstructure of TiO 2 thin films, and silver in the films is metallic Ag (Ag 0). Hydrophilic behavior of the films increases with the increase of silver content up to 5 vol% Ag and then decreases. A suitable amount (around 5 vol% Ag) of silver addition can significantly enhance the hydrophilicity of TiO 2 films. The hydrophilic behavior of the films is discussed in terms of the synergic effects of defective site, energy gap, surface roughness, and grain size.

Enhanced photocatalytic activity of silver nanoparticles modified TiO 2 thin films prepared by RF magnetron sputtering

Ag-TiO 2 nanostructured thin films with silver volume fraction of 0–40% were prepared by RF magnetron sputtering. The microstructure, surface topography, and optical properties of the films were characterized by X-ray diffractometer, transmission electron microscope, and ultraviolet–visible spectrophotometer. Photocatalytic activity of the films was evaluated by light-induced degradation of methyl orange (C 14H 14N 3NaO 3S) solution using a high pressure mercury lamp as lamp-house. The relation of photocatalytic activity and silver content was studied in detail. It is found that silver content influences microstructure of TiO 2 thin films, and silver in the films is metallic Ag (Ag 0). Photocatalytic activity of the films increases with increasing silver content up to 5 vol.% Ag and then decreases to values significantly still bigger than that of pure TiO 2 thin films. Silver nanoparticles significantly enhance the photocatalytic activity of TiO 2 films. The better separation between electrons and holes on silver modified TiO 2 thin films surface allowed more efficiency for the oxidation and reduction reactions. The enhanced photocatalytic activity was mainly attributed to the decrease of energy gap of the films and the increase of oxygen anion radicals O 2 − and reactive center of surface Ti 3+ on silver modified TiO 2 thin films surface.

Three-phase polymer–ceramic–metal composite for embedded capacitor applications

This paper addresses the materials and processes for printed wiring board compatible embedded capacitor using ceramic, polymer and metal. The Ca[(Li 1/3Nb 2/3) 0.8Ti 0.2]O 3− δ (CLNT)–epoxy–silver, three-phase composites were prepared by two step mixing and thermosetting technique. The dielectric properties of the three-phase composites were investigated in terms of volume fraction of silver, temperature and frequency. The dielectric properties of epoxy–CLNT composites were compared with theoretical predictions. The relative permittivity of the three-phase composites increased with silver loading. Addition of 0.28 volume fraction of silver increases the relative permittivity of epoxy–CLNT composites from 8 to 142 at 1 MHz. This composite is flexible and can be fabricated into various shapes with low processing temperature.

A mechanism for enhanced hydrophilicity of silver nanoparticles modified TiO 2 thin films deposited by RF magnetron sputtering

Ag–TiO 2 nanostructured thin films with silver volume fraction of 0–40.0% have been deposited on silicon and quartz substrates by RF magnetron sputtering. Their crystal texture, surface topography, and hydrophilicity have been characterized by X-ray diffractometer, transmission electron microscope, and water contact angle apparatus. The relation of hydrophilic property and silver content has been studied in detail. It is shown that silver content influences crystal texture of TiO 2 thin films, and silver in the films is simple substance (Ag 0). Hydrophilicity of the films increases with increasing silver content up to 5 vol% Ag and then decreases. A suitable amount (around 5.0 vol% Ag) of silver addition can significantly enhance the hydrophilic behavior of TiO 2 films. The mechanism can be attributed to the increase of oxygen anion radicals O 2 − and reactive center of surface Ti 3+, and the better separation between electrons and holes on the films surface.

Percolation phenomenon in barium samarium titanate–silver composite

Ba 4Sm 9.33Ti 18O 54–Ag (BST–Ag) composites were prepared by a solid-state ceramic route and its dielectric properties were investigated in the vicinity of percolation threshold. The structure and microstructure of the composites were analyzed by X-ray diffraction along with optical and scanning electron microscopy observations. The effects of silver content and frequency on the dielectric properties of BST–Ag composites were studied using a LCR meter. The relative permittivity ( ε r) of the composite increases with silver content below the percolation limit and is in agreement with power law. A 0.14 volume fraction of silver loading increases the relative permittivity of the composite from 50 to 450 at 10 kHz. Addition of 0.15 volume fraction of silver increases the relative permittivity of the composite in the order of 10 5. It is found that the giant relative permittivity is almost constant for frequencies from 1 kHz to 1 MHz. This high ε r composite offers the perspectives for application in electromechanical devices.

Effect of sintering temperature on the percolation threshold and the dielectric properties Ca[(Li 1/3Nb 2/3) 1–x Ti x]O 3–δ – Ag composite

The Ca[(Li 1/3Nb 2/3) 1– x Ti x ]O 3– δ + Ag (CLNT + Ag) composites were prepared by solid state ceramic route and its dielectric properties were investigated as a function of silver loading. The sintering temperature of the CLNT ceramics was lowered to 950 °C/2 h by the use of (Li 2CO 3–B 2O 3–SiO 2) LBS glass additive. The effect of sintering temperature on the percolation threshold of ceramic–silver composites was investigated. The dielectric properties were systematically characterized in terms of relative permittivity, dielectric loss and conductivity with volume fraction of silver, frequency and temperature. The relative permittivity of the composite increases with silver content and it is in good agreement with power law below the percolation limit. Addition of 0.17 volume fraction of silver increases the relative permittivity of CLNT + 5 wt% LBS from 32 to 270 at 1 MHz. The maximum increase in relative permittivity ( ε r ≈ 4 × 10 5) with low dielectric loss (tan δ ≈ 10 –2) at 1 MHz was observed for 0.18 volume fraction of silver. The relative permittivity of the composites was found to be independent of temperature for all the range of silver loading investigated in this study. CLNT + 5 wt% LBS with 0.18 volume fraction of Ag shows the capacitance density of 0.265 μF/cm 2 and 21.5 μF/cm 2 at 1 MHz and 100 KHz, respectively. This offers the perspectives for application of this composite in decoupling and electromechanical devices.

Giant Permittivity of a Bismuth Zinc Niobate–Silver Composite

Bismuth zinc niobate–Silver (BZN–Ag) composites were prepared by the solid‐state ceramic route. The sintering temperature of BZN–Ag composites was lowered to 850°C/2 h. The structure and surface morphology of the composites were investigated using X‐ray diffraction and optical microscope. The dielectric and conducting properties of the composites were systematically investigated with the volume fraction of silver in the frequency range from 1 KHz to 1 MHz. The dielectric constant of the composite increases with the silver content and is in good agreement with the power law below the percolation limit. Addition of 0.14 volume fraction of silver increases the dielectric constant of BZN+2 wt% B2O3 from 150 to 2350 at 1 MHz. However, 15 volume percentage of silver loading results in a large permittivity of (ɛr)≈105 with a low dielectric loss (tan δ≈10−2) at 1 MHz. Subsequent increase in silver loading decreases the dielectric constant. The BZN–B2O3–Ag composite with large permittivity may find applications in electromechanical and tunable devices.

Silver Particle Carbon-Matrix Composites as Thick Films for Electrical Applications

Silver particle (3 μm) carbon-matrix composites in the form of thick films (around 100 μm thick) on alumina, as prepared from pastes comprising silver and mesophase pitch particles (14 μm), have been attained. The films on alumina were fired at 650°C in nitrogen to convert pitch to carbon. The volume electrical resistivity attained ranged from 10−5 Ω cm to 104 Ω cm, depending on the silver volume fraction. The percolation threshold was 12 vol% silver.

Deposition of “Polysiloxane” Thin Films Containing Silver Particles by an RF Asymmetrical Discharge

AbstractThe aim of the present work is to produce silver‐containing SiCxOyHz thin films by using simultaneous sputtering of silver and plasma polymerization in an HMDSO plasma. The ratio of plasma polymerization to sputtering was adjusted by using a pulsed flow rate of the hexamethyldisiloxane precursor, which permitted an accurate control of the co‐deposition process. The presence of silver in the gas phase was detected by optical emission spectroscopy. The silver volume fraction was controlled over a wide range by superimposing physical sputtering onto the polymerization process taking place simultaneously within a very low and narrow range of HMDSO plasma pressure. The polymer matrix structures were analyzed by several techniques. FTIR spectra revealed the presence of SiOSi, SiCSi, SiCH3 and CC groups whose amount varied with the silver content. TEM analysis showed Ag nanoparticles with sizes varying from 4 to 70 nm depending on the silver volume fraction.magnified image

Fabrication and sintering effect on the morphologies and conductivity of nano-Ag particlefilms by the spin coating method

By adjusting the rotating speed and colloidal concentration in the spin coating of silvernanoparticles onto a glass substrate, the coating density could be varied from1.5 × 10−6 to1.1 × 10−4 g cm−2, or in other words from a dispersed distribution to multi-layered close packedfilms. The coating density was found to be proportional to the volume fractionof silver colloids and inversely to the rotating speed to the 0.442 power. Themulti-layered films were further investigated for sintering behaviour. Our resultsindicated that the film started to exhibit a noticeable sintering effect at about100 °C, and at the same time it became electrically conductive. As the treatmenttemperature increased further, the film resistivity reached a minimum value at250 °C and finally became insulating again when the temperature was over400 °C due to silver coalescence into large particles and breaking up of the conductive paths.Smaller silver nanoparticles, however, would exhibit a similar phenomenon but at lowertemperatures.

Effect of nano-sized silver particles on the resistivity of polymeric conductive adhesives

In this work, conductive adhesives were made by adding micro-sized silver flakes, mixed-sized silver particles or nano-sized silver colloids to the polyvinyl acetate (PVAc) emulsion. Film resistivity was then measured as a function of silver volume fraction. Our results indicated that the addition of nano-sized silver colloids to micro-sized Ag flakes usually increased its resistivity, probably due to increased contact resistance. Only near the percolation threshold, would the addition of nano-sized silver particles decrease the resistivity by helping to form the conductive path. Films made with only nano-sized silver colloids at the volume fraction of 0.848 showed a rather low resistivity of 1.93×10 −4 Ω cm. Increase in heating temperature helped to form necks between particles and thus improve the conductivity to some extent.

Optical study of Ag-TiO2nanocermet thin films prepared by R.F. co-sputtering

The optical properties of Ag-TiO 2 nanocermet thin films are studied with the aim of optical filtering applications. Beyond the classical properties of cermets with noble metal inclusions predicted by the effective medium theories, the optical properties of Ag-TiO 2 nanocermets deposited by R.F. co-sputtering are governed by their columnar morphology and the under-stoichiometry of the TiO 2 matrix. A careful experimental analysis of the different parameters and effects involved in the optical response of these nanocermets is performed both on TiO 2 and Ag-TiO 2 : film thickness, silver volume fraction, thermal treatments, oxidation. The influence of these parameters on the surface plasmon resonance and the infrared transmission of the nanocermet thin films is optimized.

Low‐Temperature Sintering and High‐Strength Pb(Zr,Ti)O3‐Matrix Composites Incorporating Silver Particles

Lead zirconate titanate based composites containing silver particles were fabricated from commercially available PZT and Ag2O powder mixtures. Densification behavior and mechanical and dielectric properties were evaluated as a function of the volume fraction of silver. No unwanted reaction phases between the PZT matrix and silver could be detected in the X‐ray diffraction analysis. The added silver particles were homogeneously dispersed in the matrix. The densification of PZT was substantially accelerated by the addition of silver particles. Mechanical properties, e.g., fracture toughness and fracture strength, were improved by the addition of silver particles. The relative dielectric constant also increased when the volume fraction of silver was increased. This observed enhancement in dielectric constant may be associated with the effective dielectric field developed by the existence of conducting silver particles.