Silver Agglomerates Research Articles

The Inhibition of Silver Agglomeration by Gold Activation in Silver Electroless Plating

In Ag electroless plating, Ag agglomeration has been the obstacle to obtain thin Ag films. The crystallographic misfit between the substrate and Ag can accelerate Ag agglomeration. In this paper, Au, whose crystallographic characteristics are similar with those of Ag, is used as the activation material. As a result, the Ag layer was deposited in the form of layer-by-layer growth. Therefore, Ag film electrolessly deposited on a substrate activated by Au can be used to manufacture the interconnections in microelectronic devices. In this experiment, the resistivity of the Ag film was measured to , which was decreased to by the annealing process.

Oxidation behaviour of thin silver films deposited on plastic web characterized by spectroscopic ellipsometry (SE)

Silver layers were deposited on plastic web by DC magnetron sputtering using different additional oxygen inlet. Single Ag layers sputtered at an oxygen inlet below 14 sccm, which amounts to 12.3% (Ar: 100 sccm) of the whole gas flow, exhibited no noticeable change in optical properties. At 112 sccm O 2 the synthesis of Ag 2O is reached. At higher flow, a semi transparent coating was formed, which is assumed to be AgO. The dispersions for synthesized single AgO fit the resulting oxide layer, grown by a subsequent oxygen rich plasma process, very well. The modeling of plasma oxidation of silver showed, that the formation of the AgO phase is not the only reason for the degradation of silver containing layer stacks. Beside that agglomeration of silver takes place, intrinsic stresses (caused by the oxidation) resulting in partial delaminations and a dramatic increased roughness occurs.

Impact fragmentation of nanoparticle agglomerates

A method of fragmenting nanoparticle agglomerates by impaction from the aerosol phase in a single-stage impactor is described. The degree of fragmentation as a function of impaction velocity is determined by TEM image analysis of impacted agglomerates. Images of unfragmented particles are obtained by diffusional deposition in the same apparatus but operated in a different way. As an illustration, the method was applied to aerosols of silver, nickel and titanium dioxide agglomerates with primary particle diameters of between 3 and 8.3 nm (Ag), 4 nm (Ni) and 95 nm ( TiO 2) , respectively, for which we determined the influence of impact energy and primary particle size on fragmentation. For silver, the degree of fragmentation at a given impact energy decreased with primary particle size; at 3 nm hardly any fragmentation was observed. At a given primary particle size, however, the range of energies required for complete fragmentation was found to be relatively narrow, indicating a fairly uniform bond structure. These trends are reflected by a model that was devised to calculate bond strength distributions between polydisperse primary particles assuming there are only van-der-Waals interactions. Some measurements were also carried out to investigate potential effects of impact energy on primary particle size.

Removal and sequestration of iodide using silver-impregnated activated carbon.

Two silver-impregnated activated carbons (SIACs) (0.05 and 1.05 wt % silver) and their virgin (i.e., unimpregnated) granular activated carbon (GAC) precursors were investigated for their ability to remove and sequester iodide from aqueous solutions in a series of batch sorption and leaching experiments. Silver content, total iodide concentration, and pH were the factors controlling the removal mechanisms of iodide. Iodide uptake increased with decreasing pH for both SIACs and their virgin GACs. The 0.05% SIAC behaved similarly to its virgin GAC in all experimental conditions because of its low silver content. At pH values of 7 and 8 there was a marked increased in iodide removal for the 1.05% SIAC over that of its virgin GAC, while their performances were similar at a pH of 5. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analyses prior to reaction with iodide showed the presence of metallic silver agglomerates on the 1.05% SIAC surface. After the reaction, elemental mapping with EDX showed the formation of silver iodide agglomerates. Oxidation of metallic silver was observed in the presence of oxygen, and the carbon surface appears to catalyze this reaction. When the molar ratio of silver to iodide was greater than 1 (i.e., M(Ag,SIAC) > M(I,TOTAL)), precipitation of silver iodide was the dominant removal mechanism. However, unreacted silver leached into solution with decreasing pH while iodide leaching did not occur. When M(Ag,SIAC) < M(I,TOTAL), silver iodide precipitation occurred until all available silver had reacted, and additional iodide was removed from solution by pH-dependent adsorption to the GAC. Under this condition, silver leaching did not occur while iodide leaching increased with increasing pH.

Determination of Coating Thickness of DEHS on Submicron Particles by Means of Low Pressure Impaction

The increasing use of submicron and nano-scaled particles in process engineering sets a demand for new methods for the characterization of particle properties. In the present work low pressure impaction as a very sensitive method for the characterization of the coating of nanoparticles is introduced. The determination of the coating thickness is based on the change of effective density due to the differing densities of particle and coating material, As model systems the coating of spherical silver nanoparticles and agglomerates of silver nanoparticles with DEHS (di(2-ethylhexyl)sebacate) were used. A tandem differential modelling analyzer (DMA) setup served as a reference for the measurement results obtained with the low pressure impactor (LPI). The LPI showed a very high sensitivity for the coating of spherical particles. Changes of the particle radius below 1 nm could be detected. In contrast to spherical particles, agglomerated particles did not show a clear correlation between coating thickness and the change of effective density for coated agglomerates.

Electron spin resonance studies on silver atoms in imogolite fibers

The formation and stabilization of reduced silver species in imogolite have been studied by electron spin resonance (ESR) spectroscopy. Ag-loaded imogolite samples after degassing and dehydration were γ-irradiated at 77 K and monitored by ESR as the temperature increased. Some samples were exposed to methanol vapour after dehydration. It was found that imogolite shows exceptional ability to stabilize silver atoms. In dehydrated Ag-imogolite silver atoms generated at low temperature remain stable at room temperature. Silver atoms are also formed in imogolite samples exposed to methanol. However, in contrast to silver agglomeration in molecular sieves and smectites exposed to methanol there is no indication of the formation of cationic silver clusters in Ag-imogolite. It is postulated that there are special trapping sites in imogolite structure which effectively stabilize silver atoms.

Moisture degradation mechanism of silver-based low-emissivity coatings

Moisture deterioration of low-emissivity (Low-E) coatings with layer structures of oxide/silver/oxide/glass, oxide/silver/glass, silver/oxide/glass, and silver/glass were investigated. All the films were formed by r.f. magnetron sputtering. Zinc oxide (ZnO) and tin oxide (SnO2) films were used as oxide layers. The coatings were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The storage for 144h at 50°C, 95% relative humidity was adopted as a moisture test. Only the silver film formed on the ZnO underlayer showed a crystalline state of the Ag(111) peak before the moisture test. The coating with the crystalline silver layer was more stable against moisture, however the moisture test generated silver migration partly, so that shallow dimples were formed. On the other hand, the coating with an amorphous silver layer was less stable, and the moisture test changed its structure into the crystalline form and brought about strong silver agglomeration. Judging from these results, it was concluded that the silver migration induced by moisture triggered a reduction of the ZnO–Ag interfacial adhesive force and caused the moisture-induced deterioration (the peeling of the top oxide layer).

Effect of Heating Cycle on the Structure of Ag Films Deposited over Porcelain Substrates

Silver films were deposited over porcelain substrates by using flexible adhesive transfer layers. These films were produced in order to use porcelain utensils over household induction heating plates. Mixtures of different glass ceramic powders with silver powder are used to prepare the self-transfer patterns. These patterns are deposited over porcelain substrates and sintered using different heating cycles. One defect observed in such films is the presence of porosity either at the Ag/porcelain interface or inside the Ag film structure. While lower sintering temperatures produce less porosity, the microstructure of the Ag layer at lower temperatures is no longer composed of a contiguous network of large silver agglomerates. Consequently, the heating capability of the layer through electromagnetic induction is affected. Finally a sintering cycle is proposed for which the film properties are least modified with a minimum level of porosity.

Reduction and Agglomeration of Silver in the Course of Formation of Silver Nano Cluster in Poly(methyl methacrylate)

Abstract Characterization of Ag nanocluster in poly(methyl methacrylate), PMMA, and kinetic observation on the polymerization of MMA in the presence of silver(I) complex have been investigated. On the basis of these studies, it was revealed that the growing polymer radical is responsible for the reduction of Ag ion and the heat-treatment appears to play an important role for the agglomeration and the formation of Ag cluster.

Influence of metallic silver and of platinum-silver bimetallic deposits on the photocatalytic activity of titania (anatase and rutile) in organic and aqueous media

The influence of deposited silver upon the photocatalytic activity of titania in the rutile and anatase allotropic forms has been studied in three different reactions. The common feature found for these three reactions was an electron transfer from illuminated TiO 2 to silver particles. In the first reaction (platinum photodeposition). it has been shown that the initial presence of metallic silver orientates the localization of subsequent Pt photodeposits with, in particular, a 100% selectivity to Pt deposition on top of silver particles or agglomerates previously deposited on anatase. In the second reaction (2-propanol oxidation), Ag deposit was found beneficial for the activity of rutile and detrimental for that of anatase. For rutile which is less active, silver helps for the electron-hole pair dissociation. By contrast, for anatase, the negatively charged Ag particles preferentially attract photoholes and become recombination centers, thus decreasing the photocatalytic activity. For the third reaction (dehydrogenation of 2-propanol), Ag/TiO 2 catalysts were found very poorly active, as expected for a group I-B metal. However, in the additional presence of platinum deposits, Pt/Ag/TiO 2 catalysts are as active as their Pt/TiO 2 homologues, thus confirming that Pt is deposited on top of silver with good electronic contacts between both metals. The three photocatalytic reactions have common electronic processes based on the photoelectron generation on titania and the subsequent electron transfer to the metal (s).

Microstructural analysis of BSCCO-2212 wires for magnet application

Short samples of silver-sheathed BSCCO-2212 wires were quenched out of different stages of the sintering process. Microstructural studies of the phase formation have been performed. The development of the superconducting core within these wires exhibit pronounced void formation. In addition it is observed, that silver agglomerates between grains all over the ceramic core. These studies were used to optimize the preparation of BSCCO-2212 wires of medium length. For functional studies of insulation material, small test coils were built from these materials and tested in a Gifford-McMahon-cryocooler. Magnetic fields were determined by a Hall probe measurement in the temperature range of 28 to 77 K.

In situ determination of the activation energy for restructuring of nanometer aerosol agglomerates

A new approach to the kinetics of the rearrangement of aerosol agglomerates is presented. This analysis is based on the change in free energy per primary particle during restructuring. The excess free energy compared with the final state drives the agglomerate to become more compact which results in an increase in the coordination number, as estimated from the changing fractal dimension of the aerosol agglomerates The analysis was tested on agglomerates of nanometer silver and copper particles produced by an evaporation-condensation technique and by laser ablation. The assumption that the rearrangement is an activated process was supported by the results. It was concluded that the interaction between the primary particles occurs over a short range. The activation energies were one order of magnitude lower than the bond energies expected from the bulk Hamaker constants for silver and copper. Within the measured size range no significant difference in the activation energies of silver and copper agglomerates was found. A maximum in the activation energy was found for particles about 18 nm in diameter. Larger particles showed decreasing activation energy with increasing diameter. The addition of oxygen (50%) before the agglomeration of the primary particles increased the activation energy by a factor of two and shifted the maximum in the activation energy to 15 nm. The prefactor in the rate coefficient for restructuring increased by four orders of magnitude when oxygen was added

Detailed study on the characterization of silver nanocluster in poly(methyl methacrylate)

ABSTRACTSolid sol of silver in poly(methyl methacrylate), Ag/PMMA, was prepared by bulk polymerization of methyl methacrylate solution of silver (I) triflluoroacetate (AgTfa) and followed by postheating. The formation of the metallic Ag nanocluster was characterized by visible spectroscopy, and effects of the concentrations of AIBN and AgTfa and the heat-treatment duration on the formation of Ag cluster were investigated. Furthermore, based on the kinetic study of MMA in the presence of AgTfa, possible mechanism for the reduction and agglomeration of silver is proposed.

New surface layer materials from polymerized complexes of aminotriazole with transition metals

Polymerized complexes of aminotriazole with transition metals are effectively bound by mineral supports. Thermal decomposition of the silver complexes in vacuo leads to supported free silver agglomerates. These materials are interesting as potential silver catalysts.

In situ characterization and structure modification of agglomerated aerosol particles

A method based on the combination of differential mobility analysis with inductively coupled plasma optical emission spectrometry, an epiphaniometer and a condensation particle counter is presented to measure simultaneously and in situ mass, exposed surface and mobility diameter of aerosol agglomerates. The technique was applied to silver agglomerates formed by spark discharge in argon and offered the possibility to determine the exponent Df as well as the proportionality factor A in the power-law relation between agglomerate mass and size. Within the same ensemble of agglomerates, structures with Df ≈ 3 were found below a critical size and low-density fractal-like structures (Df ≈ 1.8) above. A substantial increase in the density of the agglomerates occurred by heating, even in the temperature range where the primary particle size remained unchanged. This increase was due to internal rearrangement leading to a more compact packing, as reflected in an increase of A. In the domain of fractal-like structures, heating resulted in a gradual increase from Df ≈ 1.8 to Df ≈ 3. The restructuring rate (indicated by the changing rate of the fractal dimension) was governed by the temperature and the heating time. The results show that the applied methods have the potential to tailor agglomerate shape in order to match special requirements in the production of agglomerated structures.

Silver atoms and clusters in molecular sieves and clays

Electron spin resonance (ESR) and electron spin echo modulation (ESEM) studies on small paramagnetic silver clusters generated radiolytically in molecular sieves and clays are reviewed. Special attention is paid to the role of framework structure with respect to cluster nuclearity and stability. In general, geometrical size constraints play a crucial role and molecular sieves with cage-like structures with small openings between the cages such as A and rho zeolites stabilize cationic silver clusters more efficiently than channel-like zeolite structures. In addition, other factors like total cation capacity, type of cocation and/or molecular adsorbate in the cages can affect the silver agglomeration process to a great extent. The mechanism of silver agglomeration in irradiated molecular sieves and clays based on the ESR results is described as well as the reactivity of tetrameric and hexameric silver clusters with various molecular adsorbates.

In situ characterization and structure modification of agglomerated aerosol particles

Abstract A method based on the combination of differential mobility analysis with inductively coupled plasma optical emission spectrometry, an epiphaniometer and a condensation particle counter is presented to measure simultaneously and in situ mass, exposed surface and mobility diameter of aerosol agglomerates. The technique was applied to silver agglomerates formed by spark discharge in argon and offered the possibility to determine the exponent Df as well as the proportionality factor A in the power-law relation between agglomerate mass and size. Within the same ensemble of agglomerates, structures with Df ≈ 3 were found below a critical size and low-density fractal-like structures (Df ≈ 1.8) above. A substantial increase in the density of the agglomerates occurred by heating, even in the temperature range where the primary particle size remained unchanged. This increase was due to internal rearrangement leading to a more compact packing, as reflected in an increase of A. In the domain of fractal-like structures, heating resulted in a gradual increase from Df ≈ 1.8 to Df ≈ 3. The restructuring rate (indicated by the changing rate of the fractal dimension) was governed by the temperature and the heating time. The results show that the applied methods have the potential to tailor agglomerate shape in order to match special requirements in the production of agglomerated structures.

Radiation-induced silver agglomeration in molecular sieves: A comparison between A and X zeolites

The stabilization conditions of silver atoms and clusters in hydrated and dehydrated AgNa-A and AgNa-X zeolites γ-irradiated at 77 K have been studied by ESR. It was found that silver agglomeration mechanisms in hydrated A and X zeolites are very similar and are controlled by the migration of silver atoms into the α-cages. In dehydrated zeolites agglomeration leads to completely different silver clusters in A and X zeolites. Small cationic clusters are stabilized in A zeolites and metallic clusters in X zeolites. Various factors affecting the agglomeration process in A and X zeolites are discussed.

Microstructure of Agglomerates of Nanometer Particles

ABSTRACTThe microstructure of an agglomerate can be characterized by the coordination number. The relationship between the fractal dimension and the coordination number of agglomerates of nanometer particles was investigated in experiments and computer simulations. The results for silver agglomerates formed by laser ablation agreed well with the simulations. The coordination number is low for low density fractals because of the large fraction of surface particles which have fewer bonds. The sensitivity of the coordination number to the fractal dimension increases with increasing fractal dimension.

Photochemical Formation of Colloidal Silver in the Presence of Benzophenone

Abstract An aqueous silver perchlorate–sodium dodecylsulfate (SDS)–benzophenone (BP) solution was photolyzed with either UV or near-UV light. Irradiation with 253.7 nm light, which was absorbed by both BP and silver ions, brought about the formation of collidal silver and the photobleach of BP. Peptization of colloidal silver agglomerates after prolonged irradiation was ascribed to electron injection from the benzophenone ketyl radical (BPK). The formation of colloidal silver and the photobleach of BP were also caused by irradiation with 365 nm light, which was absorbed solely by BP (sensitized reaction). A simple reaction scheme was introduced and the initial rates for the sensitized photoreduction of silver ions and the photobleach of BP were expressed in closed forms. Suitable combinations of the kinetics parameters and the extinction coefficient of colloidal silver were proposed in order to interpret the dependences of the initial rates on the reactant concentrations.