Ning Li

In this microreview, the importance of electrochemical phase formation is outlined. Further, the establishment of current transition during electrochemical nucleation and growth is explored. First, the microreaction kinetic process of electrocrystallisation and the rate-controlling steps of electrodeposition are carefully discussed. Then, the current transient formulation under electrochemical polarisation-controlled electrocrystallisation is summarised. Finally, a summary of the process for calculating the current transient formulation of nucleation and growth under diffusion-controlled electrocrystallisation is explained in detail.

A brief review is given on the current transition of the electrodeposition of materials by a mechanism of nucleation followed by diffusion-controlled growth. A short historical background to study the nucleation and growth by diffusion-controlled electrocrystallization is provided. Then, an outline of the major potentiostatic current transient modeling is given, with some comments on their relative merits. Finally, a summary of the current transition functions of nucleation and growth under diffusion-controlled electrocrystallization is given including the theoretical models that have been recently applied.

A novel cyanide-free electrolyte was used in electrodepositing Au/Co–Au nano-multilayers. Firstly, an optimised electrolyte for Au–Co alloy electrodeposition was obtained from orthogonal experiments. The effect of current density and potential values on the deposited composition was investigated. Results showed that low current density and over-potential value promoted Au deposition. A large current density and high over-potential value resulted in high cobalt concentration. The co-deposition of gold and cobalt in this study system was canonical. When the electrode potential was positive (−0.6 V, −0.7 V vs. saturated calomel electrode (SCE)), only gold was deposited; when the potential was negative (−0.8 V vs. SCE), gold and cobalt were co-deposited. Using an optimised cyanide-free electrolyte produced Au/94.07 at% Co–Au multi-layers with a gold layer of approximately 20 nm and a 94.07 at% Co–Au alloy layer of approximately 90 nm in the 5,5-dimethylhydantoin-containing, cyanide-free system.

Chronoamperometry was used to investigate phase transformations at the early stage of electrodeposition under potentiostatic stimuli. Whilst electrodeposition mostly occurs under galvanostatic stimuli, this work provides a new in situ description using chronopotentiometry to analyse phase transformations during electrodeposition. With theoretical Ohm's law electro-relationship formula derivation, a non-dimensional plot between (ΔE_min/ΔE_T)² and t/t_m was established similar to (I_t/I_max)² vs. t/t_m in the SH model. The non-dimensional plots were verified by the chronopotentiometry curve during gold electrodeposition. This work provides a new method of investigating phase transformation using chronopotentiometry during electrodeposition.

The link failure recovery is important to the Internet. For improving the performance of link failure recovery in the IP network, the software defined networking (SDN) is applied to achieve this target. The SDN is effective on solving this kind of issue. However, considering the deployment cost, only a few IP routers can be replaced by the SDN switches. Thus, to minimize the number of SDN switches, the greedy-based approach is proposed to select the most appropriate deployment locations. But the greedy-based approach has disadvantages. For addressing these disadvantages, in this paper, we proposed the search-tree based SDN candidate selection (SCS) algorithm. In this algorithm, for achieving better performance than the greedy-based approach, three algorithms are proposed, which are the search-tree based feasible solutions calculation algorithm, the most appropriate feasible solution selection algorithm, and the most appropriate designated SDN switch selection algorithm. Based on these algorithms, the performance of the search-tree based SCS algorithm is improved greatly compared with the greedy-based algorithms.

A novel chrome-free Ti–P composite film was prepared by casting a mixed solution containing titanium and phosphorus species, which is able to seal the pores on the tinplate surface. The obtained film was characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The surface porosity sealing effect on tinplates was verified by using a glow discharge spectrometer (GDS), porosity tests, and XPS. The results show that the film on the tinplates is composed of TiO₂, Ti₃(PO₄)₄·nH₂O, and FePO₄. Micropores on the tinplates are reduced apparently after film deposition, and the content of iron exposed in the pores is decreased significantly. An obvious concentration peak of phosphorus at a depth of around 0.75 μm infers that the film can penetrate into the micro-pores. The film lead to a 42.5% decrease in the surface porosity of the tinplates, exhibiting an outstanding surface porosity sealing effect in comparison with pure Ti or P films. Mechanistic analysis using XPS indicates that Ti₃(PO₄)₄·nH₂O and FePO₄ in the film play a role in sealing the surface porosity.

Electrochemical nucleation and growth of cobalt onto glassy carbon electrode (GCE) from methanesulfonic acid (MSA) electrolyte was investigated, the influence of pH and cobalt concentration on the electrocrystallization mechanism was also examined. Cyclic voltammetry experiments indicate a pH and cobalt concentration dependence of the onset potential and a deposit phase change with decreasing pH was also noted. From analysis of current transients, the diffusion coefficient of cobalt ion was estimated as 1.89 × 10⁻⁵ cm²s⁻¹. The electrocrystallization mechanism for 0.6 mol/L Co²⁺ follows the instantaneous nucleation with kinetic controlled growth and is independent of the bath pH while the mechanism for 0.2 mol/L Co²⁺ follows the progressive nucleation with diffusion controlled growth at pH = 2.0 and then goes to instantaneous nucleation with kinetic controlled growth at pH = 1.5 and exhibits a process of progressive nucleation with kinetic controlled growth with lower pH of 1.0.

Topography observation of the nanoscale passivation film on tinplate using a scanning electron microscope and an electro-optical surface profilometer showed that it was difficult to observe the true topography because of the high surface roughness of the tinplate. Topography observation using a profilometer on bright tin plating with low surface roughness and work function measurement on tinplate surface using a Scanning Kelvin Probe Microscope (SKPM) were then carried out to solve the problem. The results indicated that there was a thin chemical passivation film distributed uniformly in different areas of microscopic bulges and valleys on the tinplate surface, and the film became more uniform with longer passivation time. In comparison, the electrolytic passivation film was thick, and the distribution uniformity was poorer. Specifically, the film was thicker on microscopic bulges and thinner in microscopic valleys, and this was worse with longer passivation time. Thus, the difference in performances of the corrosion and paint adhesion of the tinplate treated with different passivation processes can be explained in terms of the topography and distribution state of the passivation film.

Potentiostatic current transient is widely used to analyze the diffusion controlled three-dimensional nucleation process. SH model has a satisfied performance for almost all potentiostatic testing. However, some deviations between experimental results and the SH model's expression at decreasing period were reported. In this paper, we describe the deviation as resulting from diffusion depth is limited in electrolytic cell. Through a stochastic model is proposed, we derive an equation to describe reaction near the electrode surface of solute ions and their migration out of the diffusion zone. The theoretical model describes a limited-diffusion process using hemispherical nucleus revealed in SH model and Brownian motion in MD model. This model give a detail description of multiple nucleation process during electrodeposition. Based on the descriptions, it can be seen that SH model is a limiting case of our model, as diffusion depth R →+∞. And the equations also reveal the relationship between SH model and our new model. In addition, our theoretical equations are powerful enough to reproduce the potentiostatic current transient curves obtained from gold electrodepositing process. This work advances earlier models a step further and gives an explanation for the deviations between experimental data and standard model's description.

In this work, we developed a new potassium permanganate oxidation modification-ion exchange-reduction (OIR) process which is a mild surface ion exchange self-metallization method to fabricate conductive silver coatings with ultra-low silver consumption on polyimide film. Firstly, a hydrophilic manganese oxide modified layer loaded with K⁺ as a novel silver ion carrier was prepared on polyimide film by potassium permanganate oxidation modification. Secondly, Ag⁺ was loaded onto the manganese oxide modified layer by the ion exchange effect. Thirdly, a conductive silver layer was fabricated successfully with the reduction of Ag⁺ and the redox dissolution of the manganese oxide modified layer by a reduction process. Finally, the silver coating prepared by the OIR method has good adhesion, an 80 nm thickness value (0.56 wt% silver consumption), and a sheet resistance value of 261 Ω sq⁻¹. At the same time, characterization of the film during the preparation process and the influence of the O, I and R process times on the performance of the silver coating were studied systematically. Compared with the traditional fabrication methods of conductive silver coatings, this new technology does not require a sintering process, causes almost no damage to the chemical structure of the polyimide molecules and leaves no residual modifier. Importantly, the silver layer prepared by this method has an ultra-low silver consumption value and better conductivity at the same time. Moreover, the silver layer fabricated by this method can be used as the bottom layer of the electroplating layer in a more economical way in flexible printed circuit boards (FPCBs) and may have many potential applications in various areas.