Reaction and nucleation mechanisms of copper electrodeposition from ammoniacal solutions on vitreous carbon

The reaction and nucleation mechanisms of the electrodeposition of copper from ammoniacal solutions were investigated by cyclic voltammetric (cv) and chronoamperometric (ca) techniques, respectively. Each experiment with both electrochemical techniques was followed by morphological studies by atomic force microscopy (AFM). With respect to pH, the studies were performed on ammoniacal solutions at pH 4, pH 6, and pH 8, each representing a characteristic predominance region in E-pH diagrams. The experimental parameters were copper concentration, scanning rate, deposition potential, and electrode conditioning. It was found that at pH 4 copper electrodeposition occurs via reduction of cupric species to cuprous, which in turn can be either reduced, or disproportionated to metallic copper. At pH 6, deposition occurs from free and complexed cupric species, while at pH 8, only cupric amine complexes are involved. Copper nucleates according to instantaneous mechanisms at pH 4, and progressive nucleation mechanisms at pH 6 and pH 8. The diffusion coefficients of the copper species involved were also determined and are reported in this study.     

Reaction and nucleation mechanisms of copper electrodeposition on disposable pencil graphite electrode

The reaction and nucleation mechanism of copper electrodeposition on disposable pencil graphite electrode (PGE) in acidic sulphate solution were investigated using cyclic voltammetry (CV) and chronoamperometry (CA) techniques, respectively. Electrochemical experiments were followed by morphological studies with scanning electron microscopy (SEM). The effect of some experimental parameters, namely copper concentration, pH, scan rate, background electrolyte, deposition potential, and conditioning surface of the electrode were described. At the surface of PGE, Cu²⁺ ions were reduced at −250 mV vs. SCE. It was found that electrodeposition of copper is affected by rough surface of PGE. The nucleation mechanisms were examined by fitting the experimental CA data into Scharifker-Hills nucleation models. The nuclei population densities were also determined by means of two common fitting models developed for three-dimensional nucleation and growth (Scharifker-Mostany and Mirkin-Nilov-Herrman-Tarallo). It was found that deposition potential and background electrolyte affect the distribution of the deposited copper. The morphology of the deposited copper is affected by background electrolyte.     

Electrodeposition of copper on Ru(0 0 0 1) in sulfuric acid solution: Growth kinetics and nucleation behavior

The electrodeposition of Cu on Ru(0 0 0 1) from 0.1 M CuSO₄/0.5 M H₂SO₄ solution has been studied by cyclic voltammetry, current-time transient measurements, and by in situ electrochemical atomic force microscopy (EC-AFM). Cyclic voltammetry measurements show that the as-prepared Ru(0 0 0 1) electrode exhibits a UPD peak, while EC-AFM data indicate a broadly terraced surface with step heights of atomic dimensions. Kinetic data show that the electrodeposition/nucleation process is not well described by 3D or 2D nucleation models. The EC-AFM data show that at potentials near the OPD/UPD threshold, Cu crystallites exhibit pronounced growth anisotropy, with lateral dimensions greatly exceeding vertical dimensions. AFM data also show that deposition at more cathodic potentials result in smaller crystallites.     

Electrochemical and AFM study of cobalt nucleation mechanisms on glassy carbon from ammonium sulfate solutions

Nucleation mechanisms of cobalt on a glassy carbon electrode (gce) from aqueous ammonium sulfate solutions were investigated through the electrochemical techniques of cyclic voltammetry (cv) and chronoamperometry (ca), coupled with atomic force microscopy (AFM) studies. The studied parameters were pH, cobalt concentration, temperature, scanning rate, and deposition potential. It was found that scanning in the cathodic direction produced two peaks, corresponding to cobalt and hydrogen reduction, respectively. Scanning in the anodic direction was characterized by cobalt dissolution, which was interrupted by formation of cobalt hydroxide, causing a second anodic peak. The amperometric study found progressive nucleation mechanisms, in contrast to the instantaneous nucleation mechanisms determined by the AFM study. An explanation for the contradictory nucleation mechanisms shown in the two studies is provided.     

Iron nucleation mechanisms on vitreous carbon during electrodeposition from sulfate and chloride solutions

Iron nucleation mechanisms from aqueous solutions onto vitreous carbon electrode were comparatively investigated in iron sulfate and iron chloride systems by utilizing the electrochemical techniques of cyclic voltammetry (cv) and chronoamperometry (ca), coupled with atomic force microscopy (AFM) studies. The investigated parameters were pH, scanning rate, iron concentration, deposition potential and temperature. It was found that iron nuclei population density decreased with increase of pH. On the other hand, the population density increased with increase of iron concentration and cathodic deposition potential. Increase of solution temperature resulted in the increase of nuclei population density in the sulfate system, while the dependence of nuclei population density on temperature in the chloride system was more complex. The experimental electrochemical data fitted the theoretical model describing progressive nucleation mechanisms, which was also confirmed by the AFM morphological studies. In addition, the atomic force microscopy was successful in determining the possible crystallographic orientations of electrodeposited iron nuclei.     

Stability of iodine on ruthenium during copper electrodeposition and its effects on the nucleation behavior of electrodeposited copper

Cyclic voltammetry, current-time-transient measurements, and X-ray photoelectron spectroscopy (XPS) have been used to study the nucleation behavior of electrochemically deposited Cu films on Ru substrates as a function of Ru pre-treatment. Pre-treatment consisted of cathodic polarization in either 1 M H₂SO₄ or in 1 M H₂SO₄ + 1 mM KI, followed by sample emersion and placement in a 1 M H₂SO₄ + 50 mM CuSO₄ plating bath. XPS measurements confirmed the presence of adsorbed I on the Ru surface following pre-treatment in the KI/H₂SO₄ solution. Cyclic voltammogram (CV) data for electrodes either as-received or pre-reduced in H₂SO₄ and then immersed in the plating solution exhibited a broad peak in the overpotential region consistent with oxide reduction followed by Cu deposition. No underpotential deposition (UPD) feature was observed for these electrodes. In contrast, the sample pre-reduced in I-containing electrolyte exhibited a narrow Cu deposition peak in the overpotential region and a UPD Cu feature centered at 80 mV vs. Ag/AgCl. Current-time-transient (CTT) measurements of Cu deposition on as-received electrodes or electrodes pre-reduced in I-free solution exhibited potential-independent kinetics that are not well described by either progressive or instantaneous nucleation models and which at long times indicate a combination of diffusion and kinetic control. In contrast, CTT measurements of deposition kinetics for samples reduced in I-containing electrolyte exhibited complex, potential-dependent behavior and that at long times indicates diffusion control. XPS results also indicated that the iodine adlayer on Ru reduced in I-containing electrolyte is stable upon polarization to at least −200 mV vs. Ag/AgCl. These data indicate that a protective I adlayer may be deposited on an air-exposed Ru electrode as the oxide surface is electrochemically reduced, and that this layer will inhibit reformation of an oxide during the Cu electroplating process. Therefore, electrochemical pre-treatment in I-containing electrolyte may be of practical utility under industrial conditions for Cu electroplating.     

Electrochemical and AFM study of nickel nucleation mechanisms on vitreous carbon from ammonium sulfate solutions

Reaction and nucleation mechanisms of nickel in ammoniacal solutions have been investigated as a function of nickel concentration, solution pH, deposition potential, temperature and conditioning potential. Electrochemical mechanisms of nickel reduction were found to be pH dependent, while their kinetics was concentration dependent. A surface film formed by anodic oxidation passivates nickel clusters preventing their further oxidation. Nickel nucleation on vitreous carbon, which proceeds according to the progressive nucleation model, shows a large degree of inhibition at both pH 6 and pH 9. Cluster sizes were larger when electrodeposition was carried out from solutions with higher nickel concentrations. The clusters were also larger at more negative deposition potentials and at higher solution pH. Cluster population density increased with the increasing solution temperature. Different activation energies for the nickel-aquo and nickel-ammino complexes calculated from Arrhenius diagram indicate that electroreduction of nickel-ammino complex is energetically more demanding. All electrochemical results were further verified by the atomic force microscopy investigations.     

The electrochemical nucleation of copper on disc-shaped ultramicroelectrode in industrial electrolyte

The understanding of the very early stage of copper crystal formation kinetics and mechanism is very important for both fundamental and applied aspects. Particularly the quality of the industrial electrolytic copper deposit can be improved and better controlled. In this paper, copper nucleation mechanism is investigated in real refinery electrolytes. The main aim is to study the influence of potential, temperature and copper concentration on potentiostatic reduction of copper ions. The model of electrocrystallization is considered on the basis of the equations describing the nucleation controlled by diffusion towards a disc-shaped ultramicroelectrode. In the present paper the rates of copper nuclei formation are estimated under different applied potential, temperature, copper and levelling agent concentrations.     

Electrodeposition of nickel oxide nanoparticles on glassy carbon surfaces: application to the direct electron transfer of tyrosinase

This work describes the performance of a tyrosinase/nickel oxide nanoparticles/glassy carbon (Tyr/NiO NPs/GC) electrode. This electrode was prepared by first applying a NiO NPs electrochemical deposition onto the GC electrode surface and then tyrosinase immobilization was applied to the surface of electrodeposited NiO NPs. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) procedures demonstrated the existence of different NiO NP geometrical structures. These geometrical structures could lead to better immobilization of proteins on their surfaces. The copper containing enzyme tyrosinase successfully achieved electrical contact with the electrode because of the unique structural alignment of tyrosinase enzyme on the nanometer-scale nickel oxide surfaces. This method could be suitable for application to nanofabricated devices facilitating better performance. It was concluded that tyrosinase can be effectively applied to nanometer-scale nickel oxide surfaces.     

Quantitative evaluation of fractionated and homogeneous nucleation of polydisperse distributions of water-dispersed maleic anhydride-grafted-polypropylene micro- and nano-sized droplets

The nucleation processes in waterborne Maleic Anhydride-grafted-Polypropylene micro- and nano-droplet suspensions have been studied. Compared to a previous report on this topic, an extended set of samples in combination with improved particle size distribution data of the samples have been used, which are both essential for the advancement of the analysis.Self-nucleation was utilized to ensure that the observed lowered fractionated crystallization (peak) temperatures – down to the extremely low value of 34 °C – are due to a lack of seeds in the droplets, which seeds for the polypropylene system used are normally active at the heterogeneous crystallization temperature of approximately 110 °C. An unusual self-nucleation behavior was observed in case of samples having a large amount of small droplets, requiring an extremely low self-nucleation temperature in order to suppress all crystallization at the lowest temperatures. Such behavior was observed for block copolymers but has not been reported so far for droplets dispersed in an immiscible matrix, polymeric or not. Another unusual behavior was observed for some self-nucleation temperatures for which apparently two different populations of self-nuclei are created that are suggestive of the α₁ and α₂ crystal structures of isotactic polypropylene.Next, two new methods are presented to quantify various crucial parameters of the nucleation process: one estimates the density of nucleants acting at different temperatures from the combination of dynamic DSC data and particle size distribution (PSD) data, and the other one focuses on the nature of the nucleation mechanism using both isothermal DSC data and PSD data, quantifying the nucleation rate at different temperatures. For the present MA-g-PP dispersions the latter method leads to the conclusion that the lowest crystallization temperatures reflect sporadic nucleation, probably by way of volume (homogeneous) nucleation.In the field of polymer crystallization, polymer dispersions are usually treated as being monodisperse, even though that is rarely the case. This simplification is inadequate for the present calculations, which is why polydispersity has been taken into account in order to quantify the density of nucleants and the kinetics of nucleation. Though in the present study DSC data are used for the calculations, the methods developed can be easily adapted to other techniques like time-resolved X-ray, rheometry and dilatometry.     

Particle nucleation for dewetting initiation of thin polymer films

A quantitative comparison between spontaneous dewetting and particle nucleation for thin (thickness = 17nm) polystyrene (PS) films on nonwettable silicon (Si) surfaces is presented both experimentally and theoretically. Performing experiments in a class 100 clean room, we found that ～ 23% of the observed dry patches formed because of dust particles, while the majority of the holes formed via the well known spontaneous dewetting process. The result was verified qualitatively by diffusion theory, which, however, predicted a diminished role for the airborne particles, leading to the conclusion that pre‐existing particles on the Si surfaces and/or the polymer solutions contribute substantially to the dewetting process. The driving force of particle motion into the polymer film is examined by placing aluminum oxide (Al₂O₃) particles on PS films. Finally, the effect of particle geometry is studied by placing gold (Au) disks on the free surface of PS films. An optically continuous PS film is found to be present around the periphery of the disk particles, even after the completion of the dewetting process in the rest of the sample. An attempt to explain dewetting inhibition at the vicinity of the micro‐disks, on the basis of molecular interactions developed in the system Au/PS/Si, is finally presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 138–145, 2005     

Electrodeposition of magnesium from the eutectic LiCl–KCl melt

Electrodeposition of magnesium in the eutectic LiCl--KCl mixture (58--42 mol%) containing different MgCl₂ concentrations was studied using tungsten as cathode material. The temperature was varied above and below the melting point of magnesium (983 K). Electrochemical techniques such as cyclic voltammetry, chronopotentiometry and chronoamperometry were employed in order to characterise the system and study nucleation and growth of the magnesium phase. With all the electrochemical techniques above mentioned, macroscopic growth of the solid magnesium deposit was observed. Liquid magnesium deposits were found to grow without giving rise to a significant increase in surface area. This may be related to lithium co-deposition and formation of Li--Mg liquid solution and the differences in interfacial properties of the cathodic deposits obtained in each case. The deposition of lithium on pre-deposited magnesium leads to the formation of Li--Mg solid alloys or to a liquid Li--Mg solution at temperatures below or above the melting point of magnesium, respectively. The diffusion coefficient of magnesium ions was determined by different electrochemical techniques. The values obtained showed the effect of macroscopic growth of the deposit in the case of solid magnesium deposits.     

Growth process of homogeneously and heterogeneously nucleated spherulites as observed by atomic force microscopy

A poly(bisphenol A octane ether) (BA-C8) was synthesized. The isothermal spherulitic growth process was studied in situ using atomic force microscopy (AFM) at room temperature. For spherulites formed by homogeneous nucleation, the growth process includes the birth of a primary nucleus, the development of a founding lamella and the growth of the founding lamella into a spherulite. An embryo below a critical size is unstable. A stable embryo grows into a founding lamella. There is only one founding lamella in each spherulite. All other lamellae originate from this founding lamella. Two eyes can be seen at the center of a spherulite. For spherulites formed through heterogeneous nucleation, many lamellae grow at the nucleus surface and propagate outward radially. The spherulites acquire spherical symmetry at the early stage of crystallization. No eyes are found for this kind of spherulites.     

Electrodeposition of CdTe thin films onto n-Si(1 0 0): nucleation and growth mechanisms

The mechanisms related to the initial stages of the nucleation and growth of cadmium telluride (CdTe) thin films on the rough face side of a (1 0 0) monocrystalline n-type silicon have been studied as a function of different potential steps that varied from an initial value of −0.200 V to values comprised between −0.515 and −0.600 V versus saturated calomel electrode (SCE). The analysis of the corresponding potentiostatic j/t transients suggests that the main phenomena involved at short times is the formation of a Te-Cd bi-layer (BL). For potentials below −0.540 V, the formation of this bi-layer can be considered independent of potential. At greater times, the mechanisms is controlled by two process: (i) progressive nucleation three dimensional charge transfer controlled growth (PN-3D)_ct and (ii) progressive nucleation three dimensional diffusion controlled growth (PN-3D)_diff, both giving account for the formation of conical and hemispherical nuclei, respectively. Ex situ AFM images of the surface seem to support these assumptions.     

Nucleation and growth of copper under combined charge transfer and diffusion limitations: Part I

The nucleation and growth of copper crystals on a glassy carbon electrode are studied under potentiostatic conditions. Current transients are recorded at different overpotentials and are interpreted in terms of the theory of progressive nucleation and growth under combined charged transfer and diffusion limitations. Data are obtained on the overpotential dependence of the stationary nucleation rate and on the size of the critical copper nuclei. The influence of ion transfer and electron transfer electrochemical reactions taking place prior to and simultaneously with the process of nucleus formation is discussed and their contribution to the total current is accounted for.     

Electrochemical nucleation and growth of copper on chromium-plated electrodes

Nucleation and growth of copper electrodeposited on chromium plated electrodes in copper sulfate electrolytes were examined, focusing on the influence of prior Cr plating conditions on the nucleation density and growth kinetics of the copper electrodeposits. The Cr-plated electrodes were made by electrodeposition of Cr on copper sheets for 2 to 60 s at 0.1 A cm^–2 in CrO₃ 350 g L^–1 + H₂SO₄ 3.5 g L^–1. Copper was then electrodeposited onto the Cr-plated electrode under potentiostatic conditions. Copper initially nucleated and grew according to a three-dimensional diffusion controlled progressive nucleation process, and later according to an instantaneous nucleation process. The period during which copper nucleation is controlled by the diffusion controlled progressive nucleation process decreases with increasing Cr plating time. The nucleation density of copper was extremely high on the 2 s Cr-plated electrode, producing an extremely fine and uniform electrodeposit. However, on the 4 s Cr-plated electrode, the nucleation density of copper significantly reduced to one hundredth of that on the 2 s Cr-plated electrode, and then decreased slightly with increasing Cr plating time (thickness of Cr layer). These results appear to be associated with the IR drop across the Cr layer, including the surface Cr oxide/hydroxide film (termed the cathode film), which significantly reduces the driving force for the electrodeposition of copper under potentiostatic plating conditions.     

Influence of thiourea on the nucleation of copper on polycrystalline platinum

The influence of thiourea on the nucleation of copper from a 0.30 M CuSO4-1 M H2SO4 solution on polycrystalline platinum electrodes covered by a copper adlayer was investigated. In the case of diffusion controlled nucleation and growth the conditioning potential, that is, the potential of the electrode prior to the application of a large negative potential step, has a strong influence on the nucleation transients. This can result in either a promotion or an inhibition of the nucleation (which is characterized by a change in the nucleation rate constant and/or the site density) depending on the applied potential and the concentration of thiourea. In the region of mixed kinetics and for a fixed value of the conditioning potential (0.175 V vs Cu2+|Cu, that is, in the region of strongest inhibition), a new and rather unexpected effect was observed. Thus, after an induction period, which is proportional to the concentration of thiourea, the current increases sharply to a much higher value, but after reaching a maximum drops again to its original value. At present there is no ready explanation for this phenomenon, which has been called 'nucleation outbursts', but it deserves more investigation because the linearity between the induction time and the concentration of thiourea might have practical applications.     

Fundamental mechanisms and phenomena of clathrate hydrate nucleation

Insights into the mechanism of hydrate nucleation are of great significance for the development of hydrate-based technologies, hydrate relevant flow assurance, and the exploration of in situ natural gas hydrates. Compared with the thermodynamics of hydrate formation, understanding the nucleation mechanism is challenging and has drawn substantial attention in recent decades. In this paper, we attempt to give a comprehensive review of the recent progress of studies of clathrate hydrate nucleation. First, the existing hypotheses on the hydrate nucleation mechanism are introduced and discussed. Then, we summarize recent experimental studies on induction time, a key parameter evaluating the velocity of the nucleation process. Subsequently, the memory effect is particularly discussed, followed by the suggestion of several promising research perspectives.     

Electrochemical deposition of platinum on fluorine-doped tin oxide: The nucleation mechanisms

We report the electrochemical formation of Pt particles on fluorine-doped tin oxide electrodes by varying the concentration of PtCl₄²⁻ ions and the overpotentials within the mass-transfer-limited region. The nucleation mechanisms are considered based on the results obtained by cyclic voltammetry, chronoamperometry, and scanning electron microscopy; the nucleation mechanism changes from progressive to instantaneous as the overpotential and the concentration increase. The physical properties of deposited Pt particles, such as particle density, size, and morphology, are also studied with the changes in overpotential, concentration of PtCl₄²⁻ ions, or both.     

Electrodeposition of nano-structured nickel-21% tungsten alloy and evaluation of oxygen reduction reaction in a 1% sodium hydroxide solution

The nano-structured nickel-21 at.% tungsten alloys were electrodeposited onto the copper substrates from unstirred sulfate-citrate-chloride-bromide-sodium tungstate electrolyte at 60 °C. The maximum particle sizes of the deposits, as estimated from the atomic force microscopy (AFM), and scanning electron microscopy (SEM), respectively were 125, 75, and 100 nm. The Tafel plot for oxygen reduction reaction in oxygenated unstirred 1% sodium hydroxide solution showed a Tafel slope of 130 mV/decade. There were minor variations in the limiting current density with a change in the particle size.