Electroless versus electrodriven deposition of silver crystals in polyaniline: Role of silver anion complexes

Electrocrystallization of silver is studied at polyaniline-coated electrodes using silver cations and two silver anion complexes (silver thiosulfate and silver–EDTA) as reducing species. Use of the silver thiosulfate complex results in a significant shift of the silver deposition potential window in the negative direction and highly impeded metal crystallization. The silver cation and silver–EDTA plating solutions allow to perform both electrodriven and electroless metal deposition. Number and size of silver crystals obtained by the two deposition methods in the different plating solutions are compared. Electroless precipitation in the silver–EDTA solution results in the highest number (10⁸ cm⁻²) of small-sized crystals. This result is discussed in terms of the special role of the EDTA anions for the redox state of the polyaniline layers. It is demonstrated that factors such as polyaniline redox charge, concentration of reducing ions and dipping time allow effective control over the amount of electroless deposited metal.     

Electroless silver deposition on Si(100) substrate based on the seed layer of silver itself

A new method for silver electroless deposition on Si(100) wafer, based on the silver itself as the seed layer, was developed. The seed layer was first deposited onto the etched wafer surface in an acidic solution of 0.005 mol l⁻¹ AgNO₃+0.06 mol l⁻¹ HF. Then the silver thin film was electrolessly deposited upon the seed layer in the electroless bath of AgNO₃+NH₃+acetic acid+NH₂NH₂ (pH 10.2). The NH₂NH₂ was taken as the reducing agent. The morphology of the seed layer and the silver film were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray analysis (EDX). The experimental results indicated that the seed layer showed excellent catalytic function for silver electroless deposition.     

Electrochemical oxidation of glucose on silver nanoparticle-modified composite electrodes

Silver nanoparticle-modified composite electrodes were prepared by electroless forming silver nanoparticles in carbon black dispersed electroless silver plating solution, and then incorporating the silver nanoparticle/carbon black mixture in a polystyrene matrix. The electrooxidation of glucose in 0.1 M NaOH was studied by using cyclic voltammetry. The electrode has surface-confined nanoparicles showing effective catalytic behavior in the studies of glucose oxidation. It showed stepwise electrocatalytic oxidation behavior clearly without suppression by high background redox current caused by inner layer silver of disk-type silver electrodes. Initially the glucose was catalytically oxidized by AgO, and then the reaction glucose oxidation intermediates with Ag₂O were followed stepwisely. Based on the cyclic voltammetric results, pulsed amperometric detection parameters for flow injection analysis were optimized for sensitive detection of glucose.     

Polyaniline–silver composites prepared by the oxidation of aniline with silver nitrate in solutions of sulfonic acids

Aniline was oxidized with silver nitrate in aqueous solutions of sulfonic acids: camphorsulfonic, methanesulfonic, sulfamic, or toluenesulfonic acids. Polyaniline–silver composites were produced slowly in 4 weeks in good yield, except for the reaction, which took place in sulfamic acid solution, where the yield was low. Polyaniline in the emeraldine form was identified with UV–visible, FTIR, and Raman spectra. Thermogravimetric analysis was used to determine the silver content, which was close to the theoretical prediction of 68.9 wt.%. Transmission electron microscopy demonstrated the presence of silver nanoparticles of ca 50 nm average sizes as the dominating species, and hairy polyaniline nanorods having diameter 150–250 nm accompanied them. The highest conductivity of 880 S cm⁻¹ was found with the composite prepared in methanesulfonic acid solution. Its conductivity decreased with temperature increasing in the 70–315 K range, which is typical of metals such as silver. The conductivity of composites prepared in solutions of other acids was lower and increased with increasing temperature. Such dependence is typical of semiconductors, reflecting the dominating role of polyaniline in the conductivity behaviour. It is proposed that interfaces between the polyaniline matrix and dispersed silver nanoparticles play a dominating role in macroscopic level of conductivity.     

Polyaniline-silver composites prepared by the oxidation of aniline with mixed oxidants, silver nitrate and ammonium peroxydisulfate: The control of silver content

Aniline was oxidized with mixtures of two oxidants, ammonium peroxydisulfate and silver nitrate, to give polyaniline-silver composites with variable content of silver in the composites. The presence of peroxydisulfate has a marked accelerating effect on the oxidation of aniline with silver nitrate. Oxidations in 1 M methanesulfonic acid produced composites in high yield. The molecular structure of the polyaniline was confirmed by UV-visible and FTIR spectra, and the polymeric character was established by gel-permeation chromatography. The content of silver varied between 0 and 70 wt.%. The silver nanoparticles were smaller than 100 nm. The conductivity of the composites was of the order of units S cm⁻¹. Only at high silver nitrate contents in the reaction mixture, the conductivity of products exceeded 100 S cm⁻¹. The conductivity of the composites sometimes increased after deprotonation of the polyaniline salt to a non-conducting base. Such conductivity behaviour is discussed in terms of the percolation model.     

Region-selective electroless gold plating on polycarbonate sheets by UV-patterning in combination with silver activating

A simple, time- and cost-effective approach for region-selective metalization of polycarbonate (PC) surface has been established by combining photoresist-free UV-patterning with tin- and amine-free silver activating and electroless gold plating. The surface of PC sheets was exposed to the UV lights emitted from a low-pressure mercury lamp through a photomask, the micro pattern on the mask being transferred to the PC surface due to the photochemical generation of carboxyl groups on the UV-exposed region. The UV-exposed PC sheets were then treated with an ammoniacal AgNO₃ solution, so that the silver ions were chemisorbed by the photochemically generated carboxyl groups. When the Ag⁺-adsorbed PC sheet was immersed into an electroless gold plating bath, shiny gold film quickly deposited on the UV-exposed region, resulting in the formation of a micro gold devices on the PC surface. The whole plating process including UV-exposure, surface activating and gold plating can be completed in about 3-4 h. Attenuated total reflection Fourier transformation infrared spectrometer (ATR-FT-IR), X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM) and scanning electron microscope (SEM) were employed to trace the surface change during the plating process. Cyclic voltammetry (CV) and Scotch^®-tape test were employed to characterize the electrochemical properties and adhesion strength of the prepared micro gold devices, respectively. The prepared micro gold electrodes were demonstrated for amperometric detection of hydrogen peroxide.     

The oxidation of aniline with silver nitrate to polyaniline-silver composites

Silver nitrate oxidizes aniline in the solutions of nitric acid to conducting nanofibrillar polyaniline. Nanofibres of 10-20 nm thickness are assembled to brushes. Nanotubes, having cavities of various diameters, and nanorods have also been present in the oxidation products, as well as other morphologies. Metallic silver is obtained as nanoparticles of ∼50 nm size accompanying macroscopic silver flakes. The reaction in 0.4 M nitric acid is slow and takes several weeks to reach 10-15% yield. It is faster in 1 M nitric acid; a high yield, 89% of theory, has been found after two weeks oxidation of 0.8 M aniline. The emeraldine structure of polyaniline has been confirmed by FTIR and UV-vis spectra. The resulting polyaniline-silver composites contain 50-80 wt.% of silver, close to the theoretical expectation of 68.9 wt.% of silver. The highest conductivity was 2250 S cm⁻¹. The yield of a composite is lower when the reaction is carried out in dark, the effect of daylight being less pronounced at higher concentrations of reactants.     

Polyaniline-coated silver nanowires

Two non-conducting chemicals, aniline and silver nitrate, dissolved in formic acid solutions, yielded a composite of two conducting products, polyaniline and silver. As the concentration of formic acid increased, an alternative reaction, the reduction of silver nitrate with formic acid to silver became dominant, and the content of silver in the composites increased. The formation of polyaniline was confirmed by UV–visible, FTIR, and Raman spectroscopies. The typical conductivity of composites was 43 S cm^?1 at 84 wt.% of silver. Silver nanowires coated with polyaniline nanobrushes are produced at low concentrations of formic acid, the granular silver particles covered with polyaniline dominate at high acid concentrations.     

Development of electroless silver plating on Para‐aramid fibers and growth morphology of silver deposits

The development of a conductive fiber with flame resistance is an urgent concern particularly in national defense and other specialized fields. Aramid fibers (para‐ or meta‐) exihibit high strength and excellent fire resistance. Electroless silver plating on para‐aramid fibers and growth morphology of silver deposits was investigated in the present work. The surface of para‐aramid fibers was roughened using sodium hydride/dimethyl sulfoxide to guarantee successful electroless plating. Two complexing agents (ethylene diamine/ammonia) and two reducing agents (glucose/seignette salt) were used for the electroless silver plating bath design. Structure and properties of the resulting silver‐deposited para‐aramid fibers were evaluated based on scanning electron microscopy, silver weight gain percentage calculation, electrical resistance measurement, crystal structure analysis, and mechanical properties test. The results showed that a higher silver weight gain was advantageous to the improvement of conductivity for the silver‐deposited para‐aramid fibers. The obtained silver deposit was homogenous and compact. Electroless silver‐plating deposits were considered to be three‐dimensional nucleation and growth model (Volmer–Weber). Black, silver gray, and white deposits appeared sequentially with progressive plating. The breaking strength of silver‐deposited para‐aramid fibers remained at value up to 44 N. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Direct preparation of silver nanoparticles and thin films in CO2-expanded hexane

Small, uniform and suspended silver nanoparticles were directly prepared in CO₂-expanded hexane by reducing a synthesized metal precursor, silver isostearate, with hydrogen but without introducing additional capping agents. By increasing CO₂ pressure, the suspended silver nanoparticles could be further deposited on a solid substrate to form silver thin film via gas antisolvent and the subsequent supercritical drying processes. The silver thin films prepared by the aforementioned method possessed a uniform thickness of about 150 nm without surface cracking and low electrical resistivity (5.64 × 10⁻⁶ Ω cm) after applying an annealing process. Due to the deposition of nano-sized silver particles, the annealing temperature could be as low as 175 °C that is lower than the softening points of many transparent polymeric substrates used for fabrication of flexible conductive films.     

Influence of copper anion complexes on the incorporation of metal particles in polyaniline Part II: Copper oxalate complex

Copper deposition at polyaniline (PAN) coated electrodes is studied using copper oxalate complexes as reducing species. It is found that a high number (3.4 × 10⁸ cm^–2) of single sized (~150 nm), regular shaped crystals can be obtained. Statistical analysis of the distances between neighbouring crystals shows deviation from a random surface distribution. This finding is discussed both in terms of origin and overlap of nucleation exclusion zones and of the influence of the finite size of the copper crystals. Experiments performed under potentiostatic conditions give evidence for instantaneous copper nucleation and growth under phase boundary transition limitations. Results concerning number, size and shape of copper crystals deposited in a similar way using three different reducing species (i.e., copper cations, copper citrate and copper oxalate complex anions) are compared. It is established that the copper oxalate complex anions allow for deposition of the largest number of small metal crystals. This result is related to both the initial oxidation state of the PAN layer in the oxalate solution and to the specific properties of the anion complex.     

Electroless silver plating on the PET fabrics modified with 3‐mercaptopropyltriethoxysilane

The feasibility of adherent silver layers onto PET fabrics by electroless plating was explored and its optimal technology for modification and electroless plating was investigated. Morphology, structure, and thermal stability of silver plating PET fabrics were characterized by scanning electric microscope (SEM), X‐ray diffraction (XRD) and thermogravitric (TG) analysis. As the silver weight on the modified fabric is 25 g/m², the electromagnetic shielding effectiveness (SE) of silver plating PET fabric is more than 30dB at the frequency ranging from 1MHz to 5000 MHz. The results show that the silver plating PET fabric has good electrical conductivity and electromagnetic shielding property. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Kinetics of electroless silver deposition using cobalt(II)-ammonia complex compounds as reducing agents

The kinetics of electroless silver deposition from solutions containing Co(II)-ammonia complex compounds as reducing agents was studied at 20 and 50 °C. The process rate depends on the solution pH and the concentration of Ag(I), Co(II) and ammonia species. Under optimum operating conditions selected a silver deposition rate up to 1.2 m h^–1 can be obtained at 20 °C with high solution stability. At elevated temperature (50 °C) the rate increases and reaches 3 m h^–1. The silver coatings obtained are of high quality, compact and bright.     

Dynamic behavior of electroless nickel plating reaction on magnesium alloys

In order to obtain better control over the quality of electroless nickel–phosphorous (EN) coatings on magnesium AZ91D alloy, the effects of metal salt concentrations, reducing agent, pH, and temperature on deposition rate were studied. The reaction orders and activation energy of the deposition were determined. The results show that the apparent activation energy (E _a) in the EN plating reaction is approximately 38.03 kJ/mol. The deposition rate increased with increasing temperature, concentration of H₂PO₂ ⁻, and pH, and decreased with increasing concentration of complexing agents. For nickel ions, the deposition rate increased gradually with increasing concentration (x) when x < 4.69 g/L. However, it decreased when the concentration exceeded 4.69 g/L. Finally, various types of the deposition reaction were also discussed. The results indicate that nickel was first deposited by replacement deposition in the initial 0.5 min, then by both replacement deposition and autocatalytic deposition in plating, and finally by autocatalytic deposition after 5 min of plating.     

The co-deposition of copper and zinc inclusion in electrodeposition of silver from silver cyanide bath

The co-deposition behavior of a trace of copper and zinc as an impurity in cyanide baths for silver plating was studied by means of a radioactive tracer. The authors selected ⁶⁴CuCN and ⁶⁵Zn(CN)₂ as a labelled compound and added it to the cyanide baths for silver plating.Each amount of copper and zinc co-deposited with silver increased with increasing copper and zinc concentration in silver plating baths and temperature. It was found that the co-deposition of copper and zinc depended on cathode potentials and was not diffusion-determining. The co-deposition of copper abruptly increased in the high current density range. In the potential range Cu co-deposition is observed with Cu reversible potential through limiting current of silver deposition, and evolution of hydrogen. At low current density, Cu and Zn co-deposition are saturated at about 6400 Å thickness of electrodeposited silver and occluded in the electrodeposits is not smooth and coarse structure is observed on it.     

The electroreduction kinetics of silver sulfite complexes

The electroreduction kinetics of silver sulfite complexes was investigated by rotation disk electrode (RDE) voltammetry, chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). The stability constants of the silver sulfite complexes, pβ₂ = 7.9 and pβ₃ = 8.53 were determined. For the series of isopotential solutions investigated, a reaction order of 0.67 was obtained, the diffusion coefficient of the silver complexes varies in the range of 3.36 × 10⁻⁶ to 5.54 × 10⁻⁶ cm² s⁻¹ and the silver degree of complexation (2.31-2.67) were found. The analysis of the RDE, CP data and EIS spectra indicate the existence of a slow stage of the silver electrocrystallization in the region of the equilibrium potential and at stronger polarization of the electrode at initial time moments.     

A comparison between chemical and sputtering methods for preparing thin-film silver electrodes for in situ ATR-SEIRAS studies

Stable silver thin films were prepared either by chemical deposition or by argon sputtering on germanium and silicon substrates, respectively, and used as electrodes for in situ infrared spectroscopy experiments with a Kretschmann internal reflection configuration. The spectra obtained for acetate anions adsorbed from neutral solutions showed a noticeable intensity enhancement (SEIRA effect). This enhanced absorption has been related to the surface structure of the films that have been characterized by ex situ STM and in situ electrochemical measurements (lead underpotential deposition, UPD). STM images of the chemically deposited silver films show mean grain sizes ranging from ca. 20 to 90 nm for deposition times between 2 and 20 min, and the absence of flat domains. On the other hand, STM images of the films deposited by argon sputtering show mean grain sizes around 30 nm for a film growth rate of 0.05 nm s⁻¹ and 70 nm for a film growth rate of 0.005 nm s⁻¹. In this latter case, atomically flat domains up to 50 nm wide have been observed. This observation is consistent with a more defined voltammetric profile for lead UPD, that indicates a higher degree of surface order. Moreover, the roughness factor obtained from the charge density involved in lead UPD in the case of the sputtered silver film is lower than that measured for the chemically deposited silver film. All these structural data can be connected with the observations on the effect of deposition conditions of the silver film on the SEIRA effect for adsorbed acetate. Maximum enhancement is observed for chemically deposited films and sputtered films at high deposition rate for which the grain size is around 40-60 nm. The increase of the grain size for the sputtered silver films deposited at decreasing deposition rates can be related to the observed decrease in the SEIRA effect.     

Synthesis and characterization of polyaniline derivative and silver nanoparticle composites

BACKGROUND: There has been a recent surge of interest in the synthesis and applications of electroactive polymers with incorporated metal nanoparticles. These hybrid systems are expected to display synergistic properties between the conjugated polymers and the metal nanoparticles, making them potential candidates for applications in sensors and electronic devices. RESULTS: Composites of polyaniline derivatives—polyaniline, poly(2,5‐dimethoxyaniline) and poly(aniline‐2,5‐dimethoxyaniline)—and silver nanoparticles were prepared through simultaneous polymerization of aniline derivative and reduction of AgNO₃ in the presence of poly(styrene sulfonic acid) (PSS). We used AgNO₃ as one of the initial components (1) to form the silver nanoparticles and (2) as an oxidizing agent for initiation of the polymerization reaction. UV‐visible spectra of the synthesized nanocomposites reveal the synchronized formation of silver nanoparticles and polymer matrix. The morphology of the silver nanoparticles and degree of their dispersion in the nanocomposites were characterized by transmission electron microscopy. Thermogravimetric analysis and differential scanning calorimetry results indicate an enhancement of the thermal stability of the nanocomposites compared to the pure polymers. The electrical conductivity of the nanocomposites is in the range 10^?4 to 10^?2 S cm^?1. CONCLUSION: A single‐step process for the synthesis of silver nanoparticle–polyaniline derivative nanocomposites doped with PSS has been demonstrated. The approach in which silver nanoparticles are formed simultaneously during the polymerization process results in a good dispersion of the nanoparticles in the conductive polymer matrix. Copyright © 2008 Society of Chemical Industry     

Electroless copper plating using Fe as a reducing agent

Although the electroless plating method is known to be an effective method for obtaining fine wiring in particular, 1 mol hydrogen gas is generated during 1 mol Cu deposition, and voids are generated in the wiring when electroless Cu plating is applied to fine wiring. To avoid the hydrogen evolution, the possibility of performing electroless Cu plating was confirmed using an inexpensive Fe^II compound as a reducing agent. The bath contains CuSO₄, FeSO₄, NaCl, ethylenediamine, sodium citrate, polyethylene glycol (PEG), and 2,2′-bipyridine. Under optimal conditions, over 1.7 μm of copper deposit with a smooth surface was obtained after 3 h of plating, which did not contain iron as an impurity. The electrical resistivity of the copper film is about 3-4 μΩ cm corresponding to that of electroplated copper films.     

Effect of sulphuric acid and copper sulphate concentrations on the morphology of silver deposit in the cementation process

The silver ion cementation on copper was investigated in the presence or absence of oxygen in solutions containing 1.85 × 10⁻⁴ M Ag⁺ at 25 °C. The influence of sulphuric acid and copper sulphate concentration (0.005-0.5 M) on the silver cement morphology was studied in details and results were linked with the previously determined kinetics data of the process. The morphology of silver deposit was found to be independent of the presence of oxygen in the system as well as the sulphuric acid concentration. Contrary, the concentration of copper sulphate strongly influenced the morphology of silver deposit. At the beginning of the cementation process silver covers uniformly the copper surface. Afterwards, a growth of dendrites is initiated on preferential parts of the surface. The growing dendrite behaves as cathodic sites, with relatively huge surface area and promotes the creation of anodic sites in a close neighbourhood. Finally, the anodic site encloses the dendrite island and develops its area inward the copper material. Copper ions at low concentration modified slightly silver dendrites but the increase in concentration up to 0.5 M Cu²⁺ leads to completely disappearance of dendrites from the surface. The lack of dendrites on the surface is a result of the competitive process that consumes additional silver ions, occurring in the bulk of the solution. The morphology of silver deposit cemented in the deoxygenated solution containing 0.5 M H₂SO₄ + 0.5 M CuSO₄ depends strongly on the mechanism of the process.