Cr~(3+)电镀溶液中Cr电结晶机理

用计时电流法研究了Ｃｒ３＋镀液中Ｃｒ在玻璃碳电极上的电结晶机理,并根据理论推导出瞬时成核和连续成核的理论模型．实验结果和理论模型的分析表明,Ｃｒ在玻璃碳电极上的沉积按瞬时成核和三维生长机理进行,其法向生长速度常数Ｋ′和混合速度常数Ｋ２Ｎ０随过电位的增大而明显增大．     

添加剂对Cu/Co多层膜电结晶成核机理及磁性的影响

在硼酸镀液中以单晶S i(111)为基底用双槽法制备Cu/Co多层膜,在镀液中分别加入了镀铜添加剂2000#和镀钴添加剂5#。探讨了镀层电结晶成核机理,在基础镀液中铜电结晶为三维连续成核过程,钴电结晶在较低电位下为三维连续成核,在较高电位下为三维瞬时成核过程。加入添加剂后,铜、钴电结晶均为三维瞬时成核过程。测试了Cu/Co多层膜的磁性能;添加剂能提高多层膜的磁性能,无添加剂的Cu/Co多层膜的巨磁阻(GMR)值约为5%,而在加入了添加剂后,其GMR值高达52%。     

柠檬酸钠体系中Ni・Fe合金的电沉积行为

采用循环伏安曲线、电化学阻抗谱、计时电流曲线等方法对柠檬酸钠体系中Ni-Fe合金的电沉积行为进行了研究。结果表明:柠檬酸钠体系中Ni-Fe合金电沉积是一个受扩散控制的不可逆过程。随着电位的增大,电沉积依次经历了电化学活化阶段、电结晶成核阶段、动力学-扩散混合控制阶段和扩散控制阶段。阴极附近未被及时消耗的FeOH+会覆盖在电极表面,阻碍金属离子扩散到电极表面放电,使电化学阻抗谱低频端存在阻挡层扩散阻抗特征。随着电位的增大,Ni-Fe合金的成核速率逐渐加快。Ni-Fe合金的成核机制在低电位下表现为连续成核,在高电位下表现为瞬时成核。     

石墨基体上电沉积铜成核机理的研究

通过循环伏安法和恒电位阶跃暂态法,研究硫酸铜-硫酸溶液中铜在石墨基体上的电沉积行为,并利用扫描电子显微镜观察石墨基体表面金属铜沉积颗粒的形态和分布。结果表明:在较正的电位区间内,铜的沉积遵从连续成核机理;而在较负的电位区间内,铜的沉积遵从瞬时成核机理。     

糖精钠对混合酸盐中电沉积镍机理的影响

采用阴极极化曲线、循环伏安曲线、恒电位暂态电流-时间曲线和扫描电镜等测试方法,对含有不同质量浓度糖精钠的某公司镀镍液(主要含Ni 65~80 g/L、Na+30~40 g/L、Cl-65~85 g/L、24SO?90~115 g/L、H3BO3 6~10 g/L、其他金属离子0.013 g/L)的电化学性能和镍在其中的电结晶行为进行了研究。研究表明,糖精钠的存在使镍的沉积电位负移,在糖精钠质量浓度为1.5 g/L时负移程度最大。镍的电结晶过程符合形核–长大机理,糖精钠不改变镍的电结晶机理,但阻碍其长大过程。随着电解液中糖精钠浓度的增加,在tmt2tm(tm表示恒电位下达到峰值电流所用的时间)时间段内的形核方式由瞬时成核转变为连续成核。随着糖精钠浓度的增加,沉积层变得平整、致密。     

钛基锡锑中间层上二氧化铅电沉积过程的研究

运用电化学手段研究了钛基锡锑中间层上二氧化铅的阳极电沉积过程.循环伏安曲线表明,二氧化铅的电沉积经历了晶核形成过程,通过恒电位阶跃暂态曲线可知,二氧化铅在Ti/SnO2-Sb2O5电极上的电沉积初始过程遵循扩散控制的瞬时成核和三维长大方式,且随着过电位的增加,电极表面上晶核数增多.     

电化学方法制备聚苯胺薄膜的生长过程研究

利用恒电位法、恒电流法、电位脉冲法,在酸性苯胺溶液中制备了聚苯胺薄膜。采用交流阻抗法（EIS）及扫描电镜（SEM）对聚苯胺生长过程进行了研究。实验结果表明,苯胺电聚合初期的生长为电化学动力学控制下的三维瞬时成核过程,整个聚合过程包括形核孕育期、电化学控制瞬间成核期、扩散控制瞬间成核期、一维径向连续成核期和一维轴向连续成核期5个特征区,生长过程可分为3个阶段,分别形成球状、网状纳米纤维和纳米棒结构。     

ChCl-EG低共熔溶剂中Ni的电沉积行为研究

对氯化胆碱-乙二醇(Ch Cl-EG)低共熔溶剂中Ni的电沉积行为进行研究。采用循环伏安法和计时电流法研究了Ch Cl-EG低共熔溶剂中电沉积Ni的电化学行为、成核生长机理,利用扫描电子显微镜(SEM)、能谱分析(EDS)对电沉积得到的镀层进行微观形貌和元素组成分析。结果表明,ChCl-EG低共熔溶剂的电化学窗口为2.55V,在ChCl-EG低共熔溶剂中镍的氧化、还原电位分别是0.1V、-0.96V,还原过程为一步还原,电极还原反应不可逆,镍沉积的成核机理属于三维瞬时成核,得到的镍镀层平整、致密。     

电沉积工艺对p-CuSCN薄膜结构及半导体性质的影响

以乙二胺四乙酸二钠(ethylenediamjn tetraacetic acid disodium,EDTA)为鳌合剂,在水溶液络合体系中采用电沉积法制备了CuSCN半导体薄膜,应用电子隧穿成核和表面态热激发机理以及Mott-Schottky曲线分析了沉积电位和温度对薄膜结构和半导体性质的影响.结果表明:室温下,价带电子隧穿产生的电流与表面态空穴热激发电流在同一数量级,表面态空穴热激发电流不随电位改变,价带电子隧穿电流的变化趋势反映了整体电流的变化.随着阴极电位的升高,由于价带电子的隧穿几率变化,晶粒尺寸先减小后增大;半导体空穴浓度减小,p型性质减弱.由于沉积反应受活化能控制,在高温条件下主要表现为晶粒生长,导致晶粒尺寸增大,薄膜致密度降低;同时也使半导体空穴浓度减小,p型性质减弱.     

钼在KF—B2O3—K2MoO4熔体中的电沉积研究

采用计时电流法研究了钼在KF—B_2O_3-K_2MoO_4熔体中铂电极上的电结晶机理。实验表明,电流与时间t～(3/2)之间有很好的线性关系,从而可确认钼的电沉积是三维半球形连续成核并在扩散控制下晶核长大的过程。还讨论了钼在镍和铜基体上的电镀工艺和结果。     

Studies of carbon nucleation phenomena in molten alkaline fluoride media

The electrochemical nucleation of carbon in molten alkaline fluoride media is investigated using cyclic voltammetry and chronoamperometry in the 670-750 °C temperature range. Chronoamperometric results show that the deposition process involves progressive nucleation with diffusion-controlled growth of the nuclei, and scanning electron microscopy shows that the shape of the nuclei is hemispherical. The influence of the temperature and the overpotential on the nuclear site densities is also considered.     

Electrocrystallisation of tantalum in molten fluoride media

The electrochemical nucleation of tantalum in molten alkaline fluoride media is investigated using chronoamperometry in the 670-750 °C temperature range to optimize the operating conditions for preparing tantalum coatings for anode materials. Chronoamperometric results show that the electrodeposition process involves progressive nucleation with diffusion-controlled growth of the nuclei, which was confirmed by scanning electron microscopy. The influence of the temperature and the overpotential on the nucleation site densities is considered.Once the deposit has been obtained, plotting the roughness of the tantalum coatings as a function of the current densities reveals a minimum at about 80 mA/cm². This minimum is considered by the authors as a consequence of the progressive nucleation.     

On the influence of the nucleation overpotential on island growth in electrodeposition

Electrochemical deposition of a metal onto a foreign substrate usually occurs by an island growth mechanism. A key feature of island growth for a material M on a foreign substrate S is that the onset potential for deposition is shifted negative from the equilibrium potential for the metal ion couple. The nucleation overpotential, defined as η_n(M⁺/S) = |U_n(M⁺/S) − U_eq(M⁺/M)|, influences key aspects of deposition of a metal on a foreign substrate. Here we discuss how the nucleation overpotential influences the kinetics of island growth, the implications of the nucleation overpotential on island shape and orientation, and the consequences of the coupling between the island density (applied potential) and the island size at coalescence (grain size). We then discuss the kinetics of island growth in terms of the contributions to vertical and lateral growth. Finally, we present examples of experimental methods to manipulate the nucleation overpotential and overcome some of the limitations imposed by the nucleation overpotential.     

Two-dimensional progressive and instantaneous nucleation with overlap: The case of multi-step electrochemical reactions

Two-dimensional nucleation and growth phenomena are examined in case of multi-step electrochemical reactions accounting for the cluster overlap. Theoretical expressions are derived for the current of progressive and instantaneous nucleation at a multinuclear-monolayer, direct attachment mechanism of growth at a constant overpotential.     

Influence of potassium sodium tartrate on the initial stage of silver electrodeposition

The nucleation and growth of silver from dilute aqueous solutions of AgNO₃ was studied in the absence and in the presence of potassium sodium tartrate in the electrolyte. In both cases data were obtained for the rate of nucleation and growth of silver crystals at constant overpotential.     

Homogeneous nucleation,growth and recrystallization of discharge products on electrodes

The early state of discharge of electrodes with an electrodissolution/precipitation mechanism is investigated. A theory is proposed for quasi-classical homogeneous nucleation and the subsequent growth. Based on this theory the radii distribution function was calculated for the diffusion-controlled growth of crystallites. Recrystallization was included. The nucleation overpotential was calculated as a function of time for discharges under various conditions.     

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.     

Effect of nickel on the electrodeposition of copper

The mechanism of copper electrocrystallization from various solutions has been investigated to determine the influence of foreign cations and, particularly, of nickel. The study was performed by cyclic voltammetry and scanning electron microscopy. In sulphate solutions the Na⁺ and NH⁴⁺ cations affect the copper deposition by changing the nucleation overpotential and the presence of nickel cations makes the copper deposition easier by decreasing the nucleation overpotentials of both copper and nickel. In chloride solutions, the strong adsorption of the chloride species prevents all other influences by blocking the active sites of nucleation and growth and, therefore, Na⁺ or NH⁴⁺ addition does not modify the copper deposition. Consequently, the nickel does not modify the nucleation overpotential of copper. Whatever the solution, sulphate or chloride, the anodic behaviour of the copper-nickel codeposits are similar to the anodic behaviour of bulk Cu-Ni alloys.     

Electrochemical and AFM study of Zn electrodeposition in the presence of benzylideneacetone in a chloride-based acidic bath

The influence of benzylideneacetone (BDA) on the mechanism of zinc deposition and nucleation was studied by voltammetry, chronoamperometry and atomic force microscopy (AFM). The addition of BDA to the electrolyte solution partially inhibited (97%) the reduction of zinc at the potential E = –1.15 vs SCE/V, giving rise to an increase in the overpotential for the discharge of the metal ion. This leads to the existence of two reduction processes with different energies that involve the same species, ZnCl₄ ^2-. Analysis of chronoamperograms obtained in the absence and presence of BDA indicates that distinct nucleation mechanisms are involved during the initial stages of Zn deposition. In the absence of BDA, the transients are consistent with the model of 3D diffusion-controlled nucleation. In the presence of BDA, the transients exhibit a more complex form involving two growth processes. The first process, which occurs at short times, is explained in terms of a combination of three simultaneous nucleation processes: 2D progressive, 2D instantaneous, and 3D progressive nucleation, each limited by the incorporation of adatoms. The second process, which occurs at longer times, involves the three processes that occur at short times in conjunction with a principal contribution from a diffusion-controlled 3D nucleation mechanism. AFM imaging shows that the morphology of the deposited zinc depends on the applied electrode potential.