Nucleation and growth of copper on glassy carbon: Studies in extended overpotential interval

The nucleation and growth of copper crystals on a glassy carbon electrode are investigated at different constant overpotentials. Current transients are recorded and the number of copper nuclei is microscopically registered. The experimental data for the growth current are interpreted according to the theories of progressive and instantaneous nucleation and information is obtained on the stationary nucleation rate, the saturation nucleus number density and the exchange current density at the crystals–solution interface boundary.     

On the behaviour of molecules of the quinoline group at the water—Mercury interface: Part III. The kinetics of the isoquinoline transition in the presence of an “inert” electrolyte

The reorientation transition, which involves two distinct monolayers of isoquinoline molecules, has been investigated by using the single-potential step and the double-potential step methods under various experimental conditions.The cathodic transients correspond to a liquid → solid transition. Their morphology and half-times have been measured at various initial and final potentials, and for several isoquinoline concentrations close to the saturation value. At small overvoltages, the reorientation process is determined by heterogeneous (“instantaneous”) nucleation, while progressive nucleation and growth prevail at higher potentials. Recourse to the double-potential step method affords an efficient way of assessing separately the influence of the overvoltage on the rate constants for nucleation and growth. Determination of the critical nucleus size and the activation energy for each of the two processes has been based on an adaptation of the Brandes theory developed for two-dimensional crystallization from a supersaturated vapour phase. The kinetics are markedly dependent on the initial state, which can be easily controlled by the potential and the bulk concentration. When the potential is stepped from the region where there is superadsorption, progressive nucleation is particularly fast, while starting from a partially depleted layer gives much slower transients with extensive tailing due to diffusional hindrance.The anodic transients show consonant characteristics which indicate that the initial film can be considered as a two-dimensional solid, and that boundary defects are acting as nucleation centres, during the solid → liquid transition triggered by the potential step.     

Extracting nucleation rates from current–time transients: further comments

Nucleation rate constants, over a range of deposition potentials, are obtained for the electrocrystallisation of nickel onto a vitreous carbon electrode using the pre-pulse method. This method is based on the analysis of the early stages of two transients, one obtained as a result of the application of a single potential step, and the other resulting from the application of two potential steps (the first as a pre-pulse potential of large amplitude and short duration followed by another at which the nucleation rate is to be determined). A′-values thus obtained are compared with those estimated from the fit of the transients (each recorded at a single potential step at which A′ is to be determined) to the generalised equation derived for the model of growth of right-circular cones. The values obtained by the two methods are shown to differ from one another by about a factor of 20. Though it has been possible to obtain, with the application of two potential steps, transients which display, in the early stages of deposition, a rising current proportional to the square of the deposition time, it is shown to be impossible to describe adequately the behaviour of these transients in terms of instantaneous formation and subsequent growth of centres for the case of the deposition of nickel onto a vitreous carbon electrode. In the light of the above findings the suitability of the pre-pulse method as a means of estimating A′ has therefore been questioned in this example of electrocrystallisation. It has been shown that, even for electrocrystallisation processes where the pre-pulse method is a valid method of estimating A′, this method is, strictly speaking, applicable only to the deposition processes obtained at the lower range of potentials (at which A′ is 20 times less than the product of the radial growth rate and the square root of the density of nucleation sites). The inability of classical and atomistic theories of nucleation to arrive at plausible values for critical nucleation size has once again been demonstrated.     

Initial stages of copper electrodeposition from acidic sulfate solution in the presence of alklpyridinium hydrosulfate ionic liquids

The effect of two alklpyridinium hydrosulfate based ionic liquids(ILs)including N-butylpyridinium hydrogen sulfate(BpyHSO4)and N-hexylpyridinium hydrogen sulfate(HpyHSO4)as additives on the nucleation and growth of copper from acidic sulfate bath was investigated using cyclic voltammetry,chronoamperometric and scanning electron microscopy techniques.Results from cyclic voltammetry indicated that the two studied additives had a blocking effect on copper electrodeposition process and this effect initiated by HpyHSO4was more pronounced in comparison to BpyHSO4.Dimensionless chronoamperometric current-time transients for the electrodeposition of copper from the bath free of additives were in good accord with the theoretical transients for the limiting case of instantaneous three-dimensional nucleation with diffusion-controlled growth of the nuclei.However,the instantaneous nucleation mechanism observed in the additive-free bath was changed to a more progressive one when additives were present in the bath.Surface morphology analysis indicated that alklpyridinium hydrosulfate ILs can induce the formation of leveled and finer grained deposits by the adsorption of additive at the first stages of deposition process,leading to decrease of the nucleation and growth rate of nuclei.     

Extracting nucleation rates from current–time transients: Part III: nucleation kinetics following the application of a pre-pulse

The behaviour of the transients due to the model of the growth of right-circular cones is fully explored and compared to that of hemispheroids. The conditions that justify the use of the limiting forms of the transient equations for the so-called ‘instantaneous’ and ‘progressive’ nucleation processes are evaluated. Nucleation rates obtained from the fit of the recorded transients to the generalised equations derived for both growth models are compared. It is shown that even in those cases where electrocrystallisation proceeds via nucleation and growth of hemispheroids, analysis of the transients according to the model of the growth of cones results in estimates of nucleation rates which differ by at most a factor of three, and in most cases are as close as half the actual value.     

Current transient study of the kinetics of nucleation and diffusion-controlled growth of bimetallic phases

A model to describe the kinetics of nucleation and diffusion-controlled growth of bimetallic phases has been developed, and analytical expressions have been obtained for the elucidation of nucleation kinetics through determination of the number density N ₀ of active sites and their nucleation frequency A, from experimental current transients obtained under potentiostatic control. The validity of the model has been demonstrated with the electrodeposition of Ag–Hg phases at two distinct compositions.     

Nucleation and growtn of polythiophene films on gold electrodes

The nucleation and growth of polythiophene films on gold electrodes has been studied using potentiostatic steps. The mechanism has been deduced and estimates made of the kinetic parameters. Dissolution of the gold substrate at potentials where thiophene polymerisation occurs is suppressed by the initial rapid formation of a monolayer of polymer. The data indicate that formation of bulk film occurs by the instantaneous nucleation and three-dimensional growth of polymer on top of this monolayer. Rate constants for growth parallel to the surface on the bare gold substrate and the covering polymer layer are surprisingly very similar. Growth perpendicular to the surface is slightly more rapid, typically by a factor of 1.5–3, although it is less dependent on potential. The high density of nuclei results in their overlap at an early stage, after which growth is only possible perpendicular to the surface. Within a narrow potential range, the observation of maxima and minima in current-time transients is interpreted in terms of the “death” and “rebirth” of growing centres.     

铋在玻碳电极上电化学结晶初步研究(英文)

应用循环伏安法和计时安培法研究了铋在玻碳电极上的电结晶行为.循环伏安曲线显示了铋在玻碳电极上成核的典型特征,并表明其于玻碳电极上的电结晶是一个扩散控制过程.根据计时安培法响应曲线分析阐明了铋的浓度和过电势对成核生长机理的影响.进一步的定量测试表明该成核速率常数A和活化点密度N0随过电势增加呈现指数增大规律;扩散系数D随过电势增加呈指数衰减.以上实验结果至今未见报道.同时表明:Scharifker公式和Heerman公式均可用于本实验的理论解释.     

Density-functional theory studies on microscopic processes of gaas growth

Results for the elementary processes of MBE growth of GaAs on the frequently used GaAs(001) substrate are reviewed. We propose a bottom-up approach, where a growth model is constructed from the results of density functional theory (DFT) calculations. The implications of such a model can be tested against the information from STM images. First, the stable surface reconstructions are reviewed. Under the most commonly used conditions for MBE growth, the arsenic-rich β2 (2 × 4) reconstruction, which contains As dimers as basic building blocks, is the most stable. Next, the adsorption and diffusion of Ga atoms and As molecules on this surface is described. The DFT calculations support the picture that adsorbed Ga atoms are quite stable against re-evaporation. Thus, their mobility determines the homogeneity of the growing layer. Incorporation of Ga atoms proceeds by splitting the As dimers. We propose a model where growth proceeds in two stages: filling of trenches in the β2 (2 × 4) reconstruction, followed by nucleation of islands on the surface regions where the trenches are filled. We demonstrate how clusters of incorporated Ga atoms act as nuclei for the process of trench filling. Concerning island formation, the role of step formation energies and attachment probabilities of mobile adatoms at steps is discussed. Knowledge of these is crucial for an understanding of island shapes. Ongoing research is aiming at understanding of the microscopic mechanisms giving rise to the transition between the step-flow mode and the island-nucleation mode of growth.     

锌在玻璃碳上的电化学成核机理

线性扫描伏安法和电位阶跃法被用来研究氯化钾镀锌溶液中锌在玻璃碳上电结晶的初期阶段。发现锌在该基体上的沉积没有经历UPD过程。在本实验条件下, 成熟晶核的生长受溶液中锌离子的扩散所控制, 而晶核形成的机理依有无添加剂存在而异。通过分析恒电位暂态, 求出锌离子的扩散系数D, 以及不同过电位η下的成核速度常数A和晶核数密度N_0。A和η的关系表明“原子模型”比经典的成核模型更适合于本研究体系。N_0与η的经验关系式由曲线拟合而得。本文着重讨论了过电位和添加剂对成核作用的影响。     

Electrodeposition mechanism of nickel films on polycrystalline copper from dilute simple sulphate solutions

In this paper, we have studied the mechanism of nucleation and growth of nickel from a simple sulfate bath on polycrystalline copper (Cu) substrate. Cyclic voltammetry technique and current transients recorded during electrodeposition of nickel on Cu were used to evaluate the electrochemical deposition of nickel on copper. Results show that nickel starts to grow on copper from a typical potential of −0.7 V vs. Ag/AgCl. Increasing scan rate of cyclic voltammograms shifts the reduction peaks towards a more negative values. We plotted non-dimensional graphs according to the Scharifker-Hills theory and concluded an instantaneous nucleation and growth mechanism for nickel elecrodeposited on copper based on our experimental conditions.     

Kinetics of octadecyltrimethylammonium bromide self-assembled monolayer growth at mica from an aqueous solution

We have studied the growth kinetics of self-assembled monolayers (SAMs) ofoctadecyltrimethylammonium bromide (C18TAB) on mica below the critical micelle concentration at 22, 30, 40, and 50 degrees C. A combination of atomic force microscopy, contact angle goniometry, and transmission infrared spectroscopy was used to follow the growth processes to determine the rates involved in the growth of a C18TAB SAM on mica. The growth of a SAM consisted of four distinct processes: deposition of adsorbate molecules, growth of a disordered 2D liquid phase, nucleation of islands of an ordered 2D solid phase, and subsequent growth of the solid phase. The rates of these various processes are determined, and the activation energies for several processes were calculated including those for the adsorption onto a bare substrate (20 kJ/mol), adsorption into the saturated liquid phase (100 kJ/mol), and nucleation of islands (0.3 kJ/mol). Despite the small activation barrier to island nucleation, the nucleation rate is qualitatively slow, suggesting that entropic effects dominate the nucleation rate.     

Formation of intra-island grain boundaries in pentacene monolayers

To assess the formation of intra-island grain boundaries during the early stages of pentacene film growth, we studied sub-monolayers of pentacene on pristine silicon oxide and silicon oxide with high pinning centre density (induced by UV/O(3) treatment). We investigated the influence of the kinetic energy of the impinging molecules on the sub-monolayer growth by comparing organic molecular beam deposition (OMBD) and supersonic molecular beam deposition (SuMBD). For pentacene films fabricated by OMBD, higher pentacene island-density and higher polycrystalline island density were observed on UV/O(3)-treated silicon oxide as compared to pristine silicon oxide. Pentacene films deposited by SuMBD exhibited about one order of magnitude lower island- and polycrystalline island densities compared to OMBD, on both types of substrates. Our results suggest that polycrystalline growth of single islands on amorphous silicon oxide is facilitated by structural/chemical surface pinning centres, which act as nucleation centres for multiple grain formation in a single island. Furthermore, the overall lower intra-island grain boundary density in pentacene films fabricated by SuMBD reduces the number of charge carrier trapping sites specific to grain boundaries and should thus help achieving higher charge carrier mobilities, which are advantageous for their use in organic thin-film transistors.     

Kinetics of electrochemical nucleation and growth

A united scheme for the kinetics of electrochemical nucleation and the growth of a new phase is presented. The peculiarities of ion-transfer kinetics during electrochemical phase formation are analysed. The influence of the exchange current density at the electrolyte/cluster of the new phase interface on the nucleation rate, the nucleation induction time and the growth rate is reported.     

Influence of [BMIM]HSO4 on electrodeposition and corrosion behavior of Zn coatings from acidic sulfate bath

The effect of 1‐butyl‐3‐methylimidazolium hydrogen sulfate‐[BMIM]HSO₄ on the nucleation and growth of zinc from acidic sulfate bath was investigated at a glassy carbon (GC) electrode using cyclic voltammetry, chronoamperometric and scanning electron microscopy techniques. Dimensionless chronoamperometric current‐time transients for the electrodeposition of zinc on GC from the bath free of [BMIM]HSO₄ were in good accord with the theoretical transients for the limiting case of instantaneous three‐dimensional nucleation with diffusion‐controlled growth of the nuclei. The addition of [BMIM]HSO₄ was found to have a blocking effect on the electrodeposition of zinc and led to decrease of the nucleation and growth rate of nuclei. In addition, the instantaneous nucleation mechanism observed in the additive‐free bath was changed to a more progressive one when [BMIM]HSO₄ was present in the bath. Surface morphology analysis indicated that [BMIM]HSO₄ can induce the formation of finer grained deposits by the adsorption of additive in the first stages of deposition. The corrosion behavior of Q235 steel with coating by a thin layer of zinc in the absence and presence of [BMIM]HSO₄ was examined in 3.5% NaCl solution. The Zn coating obtained from the additive‐containing baths exhibited more excellent protection of the base metal in comparison to the additive‐free one. Copyright © 2012 John Wiley & Sons, Ltd.     

铅锑电极上PbO2生长过程的阻抗跟踪法研究

铅锑电极上ＰｂＯ_２生长过程的阻抗跟踪法研究韦国林，杨鸿兴，王家荣（上海大学嘉定校区化学系，上海，２０１８００）利用交流阻抗技术研究Ｐｂ／Ｈ２ＳＯ４体系中电化学过程，通常采用某一等效电路，并对所得的多频率阻抗频谱进行拟合处理，由此获得相关电化学信息。?..     

Kinetics of condensation of adenine at the mercury electrolyte interface

The kinetics of phase transitions of adenine adsorbed on mercury are studied by chronocoulometry and chronoamperometry from aqueous 0.1 M KClO₄ and 0.5 M NaF solutions. Experimental conditions have been selected to minimise, in the overall kinetic response, the contribution of the initial current decay, due to double-layer charging and the adsorption step. The transients corrected for these fast initial contributions present a peaked shape and can be described by the classical theory for nucleation and growth. The potential dependences of the rate constants of nucleation and growth have been obtained from double potential step experiments. The analysis of the condensation kinetics according to the classical nucleation theory leads to the evaluation of the line tension, and the Gibbs energy of formation of a critical cluster and its size.     

Electrochemical nucleation with diffusion-limited growth. Properties and analysis of transients

A general equation for the potentiostatic transient for the case of electrochemical nucleation with diffusion-controlled growth has been published recently [L. Heerman, A. Tarallo, J. Electroanal. Chem. 470 (1999) 70]. This equation essentially is a correction to the model of Scharifker and Mostany [J. Electroanal. Chem. 177 (1984) 13] but leads to quite different predictions. This paper discusses the differences between these two models with special emphasis on the analysis of experimental transients. Numerical data are presented which allow the determination of the nucleation parameters (nucleation rate constant A and site density N₀). Finally, it is shown that plots of I/I_max versus t/t_max, which are widely used in the literature for the graphical representation of experimental results, are not very sensitive and can easily lead to misinterpretation of experimental results.