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.     

An electrochemical study of the dissolution of gold in thiosulfate solutions. Part II. Effect of Copper

Thiosulfate has been considered as one of the most promising of the non-toxic alternatives to cyanide for the leaching of gold and much work has been carried out with the aim of understanding and improving the ammoniacal thiosulfate leaching process. In particular the behaviour of gold in thiosulfate solutions containing copper in the absence of ammonia has received little attention. It has been shown in this study involving electrochemical and leaching tests that copper ions catalyze not only the oxidation of thiosulfate but also the dissolution of gold in alkaline thiosulfate solutions. Electrochemical studies have shown that copper has a positive effect on the anodic dissolution of gold with increasing concentrations of copper resulting in higher dissolution rates of gold at a potential of 0.3V. Studies on the dissolution of gold powder in alkaline oxygenated thiosulfate solutions containing low concentrations of copper have shown that the role of copper in enhancing the dissolution rate of gold is possibly associated with the formation of a copper–thiosulfate–oxygen intermediate which is more reactive in terms of cathodic reduction than dissolved oxygen. The electrochemical experiments have been complemented by a leaching study which has shown that milling of gold powder in the presence of copper (added as ions, metal, or oxide) assists with the dissolution of gold in thiosulfate solutions.     

无氰镀金工艺的研究

传统的亚硫酸盐镀金液稳定性较差,就添加剂对镀液稳定性的影响进行了研究,并对镀层及镀液性能进行了测试.结果表明:镀层结晶细致,结合力、耐蚀性良好;镀液无毒、稳定性良好、分散能力和覆盖能力良好.新工艺有望取代氰化物镀金工艺,具有广阔的发展前景.     

基于计算机的镀液温度智能控制系统设计

为提高镀液温度的控制精度,以计算机为平台设计了一种镀液温度智能控制系统。设计了一种模糊PID温度控制器,可实现PID控制器参数的实时在线调整。利用动态矩阵,统计过去和当前时刻的偏差,预测未来偏差,进而得到最佳输入。最后,进行了实验研究。结果表明:镀液温度智能控制系统的收敛速率快、精度高、稳定性好,能满足电镀行业的需求,具有广阔的应用前景。     

无氰置换镀金工艺的研究

探讨了工艺参数对无氰置换镀金液稳定性及镀层性能的影响;采用正交试验优化工艺,得到了镀液稳定性好、镀层性能良好的中性无氰置换镀金工艺.此工艺含有能够减缓镀金初始时沉积速率,又能降低对镍层腐蚀的添加剂.     

Characterization of ultramicroelectrode arrays combining electrochemical techniques and optical microscopy imaging

The fabrication of chemical transducers using standard Si/SiO₂/metal microelectronic technology has given rise to a widespread development of ultramicroelectrode arrays (UMEAs) as analytical tools. The electrochemical behaviour and performance of UMEAs depend on their geometry, radius and inter-electrode distance. Therefore, a suitable design and fabrication process is required. Provided that UMEA fabrication processes are not totally efficient so far, a small fraction of the electrodes on-chip always remain passivated. In this work, Pt and Au UMEAs with three different geometries were designed and fabricated. A complete electrode characterization in terms of fabrication efficiency and analytical response is carried out by combining electrochemical techniques, transmission light and fluorescence optical imaging. Voltammetric measurements performed in ferrocyanide solutions used as a model electroactive molecule, always results in a reproducible sigmoidal response for different potential scan rate intervals depending on the electrode geometry. Optical visualization of the electrodes using transmission light microscopy relies on either electrochemical oxidation of the electrode surface or electrodeposition of gold nanoparticles. Alternatively, the anchorage of fluorescent oligonucleotide conjugates on the gold nanoparticle surface enables electrode imaging by fluorescence microscopy. Results obtained with the different techniques proposed show an excellent correlation among them. Differences in data turned out to be non-statistically relevant. It is demonstrated that less than 20% of the individual electrodes within one chip remained passivated.     

Electrodeposition of Au–Sn alloys from alkaline baths

A bath for the electrodeposition of white gold alloys of interest for the electroforming of hollow jewellery is proposed. The investigated system is an alkaline KAu(CN)₂ bath for the electrodeposition of Au–Sn alloys. The electrochemical investigations are based on cyclic voltammetry and electrodeposition experiments. Electrodeposited foils were studied from the crystallographic, compositional and morphological points of view. Co-deposition of Au and Sn gives rise to the formation of a series of intermetallic phases, which can be detected by X-ray diffraction and anodic stripping. Deposits are typically polyphasic; the phase composition generally does not correspond to the equilibrium one. Chemical compositions ranging from high-Au to high-Sn can be obtained by galvanostatic deposition at suitable current densities.     

Influence of some organic compounds on the corrosion mechanism of carbon steel (XC 38) in 3% NaCl I. dodecyl sodium phosphonate (C10H21PO3Na2) and n-undecylimidazole (C14H26N2) surfactants

The electrochemical behaviour of carbon steel (XC38) in stirred and aerated 3% NaCl solution has been investigated using a rotating disc electrode. Steady-state and transient measurements have been carried out. The influence of surfactant additives on the corrosion process is reported.     

One step gold (bio)functionalisation based on CS2-amine reaction

Dithiocarbamates have been regarded as alternative anchor groups to thiols on gold surfaces, and claimed to be formed in situ through the reaction between secondary amines and carbon disulphide. In this paper, we further exploit this methodology for a convenient one step biomolecule immobilisation onto gold surfaces. First, the reactivity between CS₂ and electroactive compounds containing amines, primary (dopamine), secondary (epinephrine), and an amino acid (tryptophan) has been investigated by electrochemical methods. Cyclic voltammetric characterisation of the modified electrodes confirmed the immobilisation of all the target compounds, allowing the estimation of their surface concentration. The best result was obtained with epinephrine, a secondary amine, for which a typical quasi-reversible behaviour of surface confined electroactive species could be clearly depicted. Electrochemical reductive desorption studies enabled to infer on the extent of the reaction and on the relative stability of the generated monolayers. Bio-functionalisation studies have been accomplished through the reaction of CS₂ with glucose oxidase in aqueous medium, and the catalytic activity of the immobilised enzyme was evaluated towards glucose, by electrochemical methods in the presence of a redox mediator. Scanning tunnelling microscopy (STM) and Atomic force microscopy (AFM) were used respectively, to characterize the gold electrodes and Glucose Oxidase coverage and distribution on the modified surfaces.     

塑料无氰仿金电镀工艺的研究

采用焦磷酸盐为络合剂研究出一种塑料无氰仿金电镀工艺。研究了镀液成分、添加剂及工艺条件对仿金镀层外观的影响,并对仿金镀层的性能进行了测试。结果表明：该工艺镀液稳定、易于维护,所得镀层光亮、结合力好、抗变色能力强。     

AC impedance study of a synthetic hydrotalcite-like compound modified electrode in aqueous solution

This paper deals with the electrochemical characterisation of Ni/Al-Cl hydrotalcite modified electrodes. The electrochemical impedance spectroscopy technique has been used in order to study the electronic and ionic conduction, both inside and on the surface of the material. The electronic and ionic contributions have been separated and the behaviour of the respective parameters has been studied as a function of the potential. In order to determine the kinetic limiting step of the overall electrochemical process we performed experiments at different temperatures, and calculated the activation energies of the electron hopping process and ion transport process. In addition we studied the behaviour of the system at different OH⁻ concentrations (pH 9.7-12.8) with the aim of clarifying the role of OH⁻ ions in the electrochemical process.     

Ultrathin polypyrrole films on self-assembled monolayers as an efficient ultramicroelectrode assay

In this work, we investigated the effect of electrodeposition of polypyrrole (PPy) films on two different self-assembled monolayers (SAMs) modified gold electrode for the electrochemical construction of ultramicroelectrode (UME). In order to obtain SAM modified surfaces, 4-mercapto-1-butanol and 11-mercaptoundecanoic acid were used. The effect of these two chains on pyrrole electropolymerization was compared. Electropolymerization of pyrrole on SAM modified Au electrode was carried out by using cyclic voltammetry (CV) and constant potential electrolysis. To investigate the UME formation, the obtained surfaces were tested in Fe(CN)₆^3−/4− redox system. UMEs were characterized using scanning electron microscopy energy-dispersive X-ray spectroscopy, attenuated total reflectance fourier transform infrared spectroscopy and electrochemical impedance spectroscopy. The designed UME was applied as an immobilization matrix to entrap a redox protein, Hemoglobin (Hb), as a model. Direct electron transfer between this protein and the fabricated thiol modified PPy based UME was achieved, which is very challenging on bare electrode surfaces. With this study, a simple, low-cost and reproducible UME production way has been successfully accomplished and Hb modified UME is promising for different bioanalytical applications, for instance; cellular hydrogen peroxide or nitrite sensing.     

Electrochemical stripping of gold from Au-Ni-Cu electronic connector scrap in an aqueous solution of thiourea

The electrochemical behaviour of a gold-plated connector from electronic scrap in aqueous thiourea solution has been investigated. An attempt was made to recover gold from scrap in a nontoxic thiourea medium by an electrochemical method rather than the traditional cyanide process. Linear sweep voltammetry indicated that thiourea extraction of gold is more efficient in acidic solution than in neutral and alkaline. Hydrochloric acid is preferable to control the pH of the solutions; the optimum concentration of thiourea is 2.5% (0.33 m). Analysis of voltammetric data yielded a critical potential (0.40 V vs SCE), which is the upper limit for significant extraction of gold from scrap. Higher potentials should be avoided in practice to prevent decomposition of thiourea and its passivation of the scrap. Electrolysis at constant potential indicated that gold was extracted selectively in the range 0.20–0.30 V vs SCE. Electrolysis at potentials either less than 0.15 V vs SCE or greater than 0.40 V vs SCE is not recommended, because of slow dissolution in the former and severe passivation in the latter.     

Compatibility Issues of Yttria‐Stabilized Zirconia Solid Oxide Membrane in the Direct Electro‐Deoxidation of Metal Oxides

Direct electro‐deoxidation of metal oxides has become quite popular in the production of metals and alloys. In this process, metal oxide cathode is directly reduced to a metal in a molten CaCl₂ salt bath. The anode material used is graphite. Over the years, graphite is reported to cause numerous process difficulties. Recently, based on the solid oxide membrane technology, yttria‐stabilized zirconia (YSZ) has been tested as oxygen ion conducting membrane for the anode. The success of using a membrane implies its long‐term stability in the bath. In this paper, it is seen that YSZ chemically degrades in a static melt of CaCl₂ or CaCl₂–CaO. The degradation occurs by leaching of yttria into solution leading to the formation of monoclinic zirconia which, being porous, reacts with the molten electrolyte to form calcium zirconate. However, on application of voltage, YSZ degrades via a different mechanism. The metallic calcium produced during electrolysis increases the electronic conductivity of the salt, apparently leading to the electrochemical reduction of zirconia to ZrO_2?x. As a result, localized pores are formed which allow the infiltration of salts. Addition of yttria to the salt is seen to prevent both the chemical and electrochemical degradation of the membrane.     

An investigation into the electrodeposition of AuCu-matrix particulate composites. Part II: Baths not containing free cyanide

In this paper we report on the electrodeposition of AuCu/B₄C composites from acid baths with gold cyanocomplexes and no free cyanide. The electrochemical behaviour of the bath and the metallographic and crystalline structures of the electrodeposited alloys were studied with and without addition of particles. Electrochemical instabilities were previously observed for free-cyanide baths and their bearing on the structure of both pure matrix and composite electrodeposits were elucidated. No instabilities were observed in the alloy deposition from the acid baths containing complexed cyanide: compositionally and structurally homogeneous microstructures were obtained both with and without particle embedding.     

A method to obtain the thermal parameters and the photothermal transduction efficiency in an optical hyperthermia device based on laser irradiation of gold nanoparticles

Optical hyperthermia systems based on the laser irradiation of gold nanorods seem to be a promising tool in the development of therapies against cancer. After a proof of concept in which the authors demonstrated the efficiency of this kind of systems, a modeling process based on an equivalent thermal-electric circuit has been carried out to determine the thermal parameters of the system and an energy balance obtained from the time-dependent heating and cooling temperature curves of the irradiated samples in order to obtain the photothermal transduction efficiency. By knowing this parameter, it is possible to increase the effectiveness of the treatments, thanks to the possibility of predicting the response of the device depending on the working configuration. As an example, the thermal behavior of two different kinds of nanoparticles is compared. The results show that, under identical conditions, the use of PEGylated gold nanorods allows for a more efficient heating compared with bare nanorods, and therefore, it results in a more effective therapy.     

Design of experiments in electrochemical microfabrication

Electrochemical material etching techniques have attracted a significant amount of attention in the “wet” metal etching arena, as the process typically involves neutral salt electrolytes and is relatively safe to operate. There are also economical and environmental advantages associated with these techniques compared with competing etching methods.A new concept of electrochemical microfabrication on substrates has been developed. In the technique the workpiece, which is the anode in the electrochemical reactor, is placed closely to a tool, which is the cathode containing the micro-pattern. Selective pattern transfer results in a higher etching rate on the areas opposing “exposed” regions of the cathode, and lower etching rates in the areas directly opposite to the areas, on the cathode, covered by an insulator.In this investigation the electrochemical micro-patterning process has been evaluated and characterised in a vertical flow system described previously in literature. The experiments were carried out using copper disk anodes and patterned cathodes in a 0.1 M copper sulphate electrolyte. A 2⁴ factorial experimental design procedure was adopted to determine the influence of process parameters on the electrochemical microfabrication process in terms of variability in pattern transfer over the electrode's surface area.     

Preparation of ZnO/Eu mixed films by electrochemical precipitation

The electrochemical preparation of europium doped zinc oxide and europium oxide/hydroxide as thin films is investigated. First, a thermodynamic study of the Eu-Cl-H₂O system has been carried out at 25 and 70 °C in order to predict the electrochemical behaviour of Eu(III) dissolved in aqueous solution containing chloride ions. A comparison of the Eu-Cl-H₂O and Zn-Cl-H₂O systems indicates the possible coprecipitation of ZnO and Eu(OH)₃ from deposition solutions containing well-adjusted Eu(III)/Zn(II) concentrations ratio. The thermodynamic predictions have been confirmed experimentally by the electrochemical co-deposition of ZnO/Eu thin films on conducting electrode substrates at −1.4 V versus MSE. The presence of europium in the film is detected for Eu(III)/Zn(II) concentration ratio at (0.6 mM/5 mM) which is lower than the predicted value. Increasing Eu(III) concentration leads to the rapid appearance of two phases: dispersed zinc oxide nanorods and, at the bottom of the rods, a covering layer containing Eu(OH)₃ and zinc. The density of ZnO rods decreases and the rod size increases with increasing Eu(III) concentration in the bath. Above 1 mM EuCl₃, a dramatic fall in the current density is observed with the formation of a less conducting ZnO/Eu mixed deposit.     

Application of EIS to assess the effect of rare earths small addition on the corrosion behaviour of Zn-5% Al (Galfan) alloy in neutral aerated sodium chloride solution

The effect of rare earth metal (Gd, Dy, Er, and Y) small additions on the corrosion behaviour of Zn-5% Al (Galfan) alloy has been investigated. The corrosion resistance of Zn-5Al-0.1Gd, Zn-5Al-0.1Dy, Zn-5Al-0.1Er, and Zn-5Al-0.1Y alloys has been assessed by electrochemical impedance spectroscopy (EIS) measurements carried out in a 0.1 M NaCl solution, at approximately neutral pH, without stirring and in contact with the air. For comparison, the electrochemical tests have also been carried out on the Galfan alloy. EIS results showed that rare earths’ addition significantly improves the corrosion behaviour of Galfan. This improvement is most likely due to enhanced barrier properties of the corrosion products layer and additional active corrosion protection originated from the inhibiting action of the lanthanide ions entrapped as oxides/hydroxides in this surface layer.     

Influence of rare earths addition on the corrosion behaviour of Zn-5%Al (Galfan) alloy in neutral aerated sodium sulphate solution

The effect of rare earth metal (Ce, Er, Y) additions on the corrosion behaviour of Zn-5Al Galfan alloy has been investigated. The corrosion resistance of Zn-5Al-1Ce, Zn-5Al-1Er and Zn-5Al-1Y alloys has been assessed by various electrochemical tests, such as corrosion potential measurements, polarization curves and electrochemical impedance spectroscopy. They have been performed in a 0.1 M Na₂SO₄ solution, at approximately neutral pH, without stirring and in contact with the air. For comparison, the electrochemical tests have also been carried out on the Zn-5Al alloy. Moreover, the surface morphology and nature of the corrosion products have been investigated. The results indicated that rare earths’ addition improves the corrosion behaviour of Galfan, the effect being more pronounced for the Er- and Y-containing alloys. The mechanism by which the corrosion resistance of Zn-5Al alloy is enhanced in presence of the rare earths is discussed.