Electrochemical and Structural Aspects of Gold Electrodeposition from Dilute Solutions by Direct Current

Abstract

The electrochemical and structural aspects of gold deposition from dilute cyanide, citrate, and phosphate‐buffered plating solutions were studied using rotating disk electrodes. Current‐potential curves were recorded galvano‐statically for 0.005M Au solutions at 60°C, and the morphology of deposits approximately 1µ thick, which corresponded to different regions of the i–V curves, was determined by scanning electron microscopy. Transmission electron microscopy was used to elucidate the early stages of growth (∼0.1µ). The cyanide system, which has an exchange current density of 0.82 mA/cm2 and a transfer coefficient of 0.7, showed the greatest tendency to form an out‐ward growth morphology consisting of fine features termed spikes. These features are responsible for the characteristic brown appearance of deposits plated under certain conditions. Increasing current density and decreasing rotation speed, in general, both favor the formation of spikes which occurs over a given range of potential false(150 normalmV<|η|<300 normalmVfalse) and not at a particular concentration of gold at the interface. The spikes, which are typically 0.1– 1.0µ in size and >108/cm2 in density, were also observed for deposits from the citrate system and to a much lesser extent in the phosphate system. At low overpotentials, a smooth, layer type of growth is formed. The formation of the various morphological features is governed by the electrode potential below the limiting current density and by mass transport near or above limiting current.

A study on the kinetics of gold nanowire electrodeposition in polycarbonate templates

“…Based on the (Fig. 4a), charge transfer coefficient is found to be 0.67 ± 0.01 which is in agreement with the value obtained by Chen and Sard [28]. Kinetic constant is a function of temperature and activation energy [26].…”

“…The value of kinetic constant is calculated to be (3.3 ± 0.1) Â 10 À4 (cm/s) based on (Fig. 4b) which is lower than that reported by Chen and Sard [28]. However, their experiments were done at higher temperature.…”

A SERS investigation of the electrodeposition of Ag–Au alloys from free-cyanide solutions

“…Extensive operative knowledge of the behaviour of these systems has accumulated during the decades and these baths are universally recognised as state-of-the-art reliable technologies. Electrochemical investigations on this topic have mainly concerned the definition of the mechanism of metal deposition from their cyanocomplexes [3][4][5][6][7]. Recently, the research has been mainly directed towards the definition of alternative cyanide-free baths [8] and several patents have been filed, chiefly regarding the use of sulphite, thiourea, thiosulphate or other sulphorated compounds as metal ligands; a comprehensive list of the patent literature would be well beyond the scope of this paper.…”

Prediction of electrodeposition rates from an impinging jet

“…Electroplating of gold can be performed from a variety of aqueous solutions containing a variety of additives that are known to have various influences on the deposited metal layer (see, for example, Cheh and Sard, 1971;Bindra et al, 1989), as well as the electro-chemical properties of the solution. In general, the aqueous solution contains excess inert electrolyte such as potassium and citrate ions, which do not take part in the reaction at either electrode, but do migrate within the electric field and thereby act to carry the majority of current within the bulk of the solution.…”

“…In general, the aqueous solution contains excess inert electrolyte such as potassium and citrate ions, which do not take part in the reaction at either electrode, but do migrate within the electric field and thereby act to carry the majority of current within the bulk of the solution. Gold is generally present in the solution (Cheh and Sard, 1971) as the negatively charged ion gold dicyanide Au(CN),-and normally may be regarded as a minor ionic component since typical concentrations are 0.1 M. As a gold dicyanide ion approaches the cathode surface, the intense field in the electrochemical double layer acts to promote the forward reaction for The liberated gold ions are then deposited on the cathode according to the reaction while the cyanide ions combine with hydrogen in solution to form hydrogen cyanide gas. Some evolution of hydrogen gas may also occur at the cathode, but this typically only accounts for 1% or less of the total current.…”