Controlled crystallite orientation in ZnO nanorods prepared by chemical bath deposition: Effect of H2O2

ZnO nanorods with controlled crystallite orientation are grown on glass substrate by chemical bath deposition (CBD) method via hydrogen peroxide (H₂O₂) route. The crystallite orientation in the film is successfully controlled by varying content of H₂O₂ in the bath solution. The crystallites became increasingly oriented as content of H₂O₂ in the bath solution increased, resulting in the formation of vertically aligned ZnO nanorods. The possible growth mechanism for the vertically aligned ZnO nanorods is proposed. The influence of content of H₂O₂ in the bath solution on structural, surface morphological, electrical and optical properties is studied and reported.     

Effect of refluxing time on the morphology of pencil like zinc oxide nanostructures prepared by solution method

This paper presents the fabrication of pencil like zinc oxide nanorods by solution method using precursor zinc acetate di-hydrate (Zn(Ac)₂.2H₂O) and alkali sodium hydroxide (NaOH) at a very low refluxing temperature (75 °C) for different ageing/ refluxing (12 h, 24 h, 36 h, 48 h and 60 h) time intervals. The morphological observation was carried out by using Field Emission Scanning Electron Microscopy (FESEM). The FESEM revealed that as the aging/refluxing time increased, the size (length and diameter) of the zinc oxide nanorods also increased. Furthermore, the morphology and crystallinity of the products grown were also confirmed by Transmission Electron Microscopy (TEM), high-resolution TEM, and Selected Area Electron Diffraction (SAED) patterns, which indicated that grown pencils grew along a [0001] direction with an ideal lattice fringe distance of ∼0.52 nm. The optical properties of the grown pencil-like zinc oxide nanorods were characterized by using UV-vis spectroscopy. Strong absorbance peaks were observed at ∼375 nm to 378 nm, which is the characteristic peak for the wurtzite hexagonal phase of ZnO. The FTIR spectroscopic measurement showed a standard peak of zinc oxide in the range of 428 cm⁻¹ to 520 cm⁻¹. Additionally, on the basis of chemical and morphological analysis, we have also proposed a possible growth mechanism for pencillike zinc oxide nanostructures.     

Electrodeposition of copper on a copper single-crystal (111) plane in the presence of thiobarbituric acid

The modification of the growth behaviour and changes in the electrokinetic parameters which occur during the electrodeposition of copper on the copper (111) plane and polycrystalline copper from an acid copper sulphate bath containing 2-thiobarbituric acid were investigated at various current densities. At low current densities (0.1 – 0.5 mA cm^-2) transitions from pyramids to layers, to ridges and then to polycrystalline growth were observed with an increase in the concentration of 2-thiobarbituric acid. At higher current densities (7.5 – 10 mA cm^-2) the change was from pyramids to truncated blocks, to ridges and finally to a polycrystalline deposit. Levelling of the grains was observed at all current densities on a polycrystalline substrate. The electrokinetic parameters have been correlated with the morphological changes and transport mechanisms proposed for different concentrations of the additive.     

High-quality vertically aligned ZnO nanorods synthesized by microwave-assisted CBD with ZnO-PVA complex seed layer on Si substrates

We successfully synthesized vertically aligned zinc oxide (ZnO) nanorods on seeded silicon substrates using chemical bath deposition assisted by microwave heating. ZnO nanorods were grown on seed layers of ZnO-polyvinyl alcohol (PVA) nanocomposites spin-coated on p-type Si (1 1 1). The nanorod's diameter was found to be dependent on the annealing temperature of the ZnO-PVA seed layer. We produced ZnO nanorods with diameters in the range of 50-300 nm from five groups of seed layers annealed at 250 °C, 350 °C, 380 °C, 450 °C, and 550 °C. The nanorods were examined with X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy, which revealed hexagonal wurtzite structures perpendicular to the substrate along the z-axis in the direction of (0 0 2). Photoluminescence measurements revealed high UV emission at a high I_UV/I_vis ratio of 175. We also conducted Raman scattering studies on the ZnO nanorods to estimate the lattice vibration modes.     

Growth and optical properties of ZnO nanorods prepared through hydrothermal growth followed by chemical vapor deposition

We report on the synthesis of high-quality ZnO nanorods by combining hydrothermal growth (HG) and chemical vapor deposition (CVD) processes. Vertically aligned and closely packed ZnO nanorods were grown by HG on a sputtered ZnO seed layer on a SiO₂/Si (0 0 1) substrate. The top surface of the HG-prepared ZnO nanorods showed very flat surfaces compared with that of the sputtered ZnO seed layer. Therefore, the HG-prepared ZnO nanorods were used as a new alternative seed material for the CVD growth of the ZnO nanorods. Vertical ZnO nanorods were grown by CVD on both the new HG-prepared nanorod seed material and the sputtered ZnO seed layer. The CVD-prepared ZnO nanorods on new HG-prepared nanorod seed material showed better crystalline quality and superior optical properties than the CVD-prepared ZnO nanorods on sputtered seed layer. The former showed negligible deep-level emissions at room temperature photoluminescence measurements. The intensity ratio of near-band-edge emissions to deep-level emissions from the former was about 910, but that from the latter was about 151. This implies that the HG-prepared ZnO nanorods can be used as a promising new seed material for nanostructure synthesis.     

Electrocrystallization of nanocrystallite calcium phosphate coatings on titanium substrate at different current densities

Calcium phosphates were electrocrystallized on titanium substrate by electrochemical deposition technique, in which the electrolyte was 0.167 M CaCl₂ and 0.1 M NH₄H₂PO₄. Different current densities (0.375, 1.5, 3, 6 mA/cm²) were applied. The pH of the solution after mixing of equal volumes was 4.6. The surface morphology, chemical composition and phase identification of the coatings were investigated by scanning electron microscopy associated with an energy dispersive spectrometer (SEM-EDXS) and X-ray diffractometry (XRD). Effects of the current density on the morphology and the structure of the coating were also discussed.The results showed that at all current densities tested, the coating is brushite (dicalcium phosphate dihydrate CaHPO₄ · 2H₂O). Furthermore, the results showed that coating thickness and weight gain are increased and the morphology changed with increasing deposition current density (from 0.375 to 6 mA/cm²). On contrary, thickness and weight gain are decreased with sodium hydroxide treatment. NaOH treatment converts brushite of Ca/P ratio 1:1 to hydroxyapatite of Ca/P ratio of 1.667. So, chemical analysis of the solution shows soluble P₂O₅ content. Coating thickness at 6 mA/cm² was about 20 and 30 µm with and without treatment, respectively. It decreased to about 9.5 and 12 µm at 0.375 mA/cm² current density, with and without treatment, respectively. However, the formed phase is not changed with increasing current density. In addition, it is found that, even at high current density (6 mA/cm²), no hydroxyapatite was directly electrocrystallized due to low corresponding potential (less than 5 V) and low corresponding voltage (468 mV).     

Field emission enhancement of ZnO nanorod arrays with hafnium nitride coating

Vertically well-aligned single crystal ZnO nanorod arrays were synthesized and enhanced field electron emission was achieved with hafnium nitride (HfN_x) coating under proper sputtering condition. HfN_x films with various composition have been coated on ZnO nanorod arrays using a reactive direct current (DC) magnetron sputtering system. Morphology and crystal configuration of the ZnO nanorod arrays were investigated by scanning electron microscopy and X-ray diffraction. The field emission properties of the coated and uncoated ZnO nanorod arrays were characterized. The as-grown ZnO nanorod arrays showed a turn-on electric field of 6.60 V μm^− 1 at a current density of 10 μA cm^− 2 and an emission current density of 1 mA cm^− 2 under the field of 9.32 V μm^− 1. While the turn-on electric field of the coated ZnO nanorod arrays sharply decreased to 2.42 V μm^− 1, an emission current density of 1 mA cm^− 2 under the field of only 4.30 V μm^− 1 can be obtained. A method to accurately measure the work function of the coated films was demonstrated.     

Influence of Chloride Ion in Acid Tin Methanesulphonate Electrolytes

The effects of trace amounts (<500 mg l^?1) of chloride ions in acid tin methanesulphonate plating solutions are presented. Thermodynamic calculations show the main species in the stannous methanesulphonate electrolytes is stannous ion and soluble complexes of Sn(II)-Cl are present. Solubility calculations show no formation of an insoluble Sn(II)-Cl complex. Electrochemical studies reveal the role of chloride ion is significant in inhibiting stannous reduction in low current density areas and only at very high Cl^? concentrations where the current is kinetically controlled. At typical plating current densities of about 20 mA cm^?2 to 40 mA cm^?2, the current is under diffusion control and commercial plating lines should not expect any difficulties from trace amounts of chloride in the electrolyte during tin plating.     

Influence of Gas Flow Rate for Formation of Aligned Nanorods in ZnO Thin Films for Solar-Driven Hydrogen Production

ZnO thin films have been deposited in mixed Ar/N₂ gas ambient at substrate temperature of 500°C by radiofrequency sputtering of ZnO targets. We find that an optimum N₂-to-Ar ratio in the deposition ambient promotes the formation of well-aligned nanorods. ZnO thin films grown in ambient with 25% N₂ gas flow rate promoted nanorods aligned along c-axis and exhibit significantly enhanced photoelectrochemical (PEC) response, compared with ZnO thin films grown in an ambient with different N₂-to-Ar gas flow ratios. Our results suggest that chamber ambient is critical for the formation of aligned nanostructures, which offer potential advantages for improving the efficiency of PEC water splitting for H₂ production.     

Effect of growth time on morphology and photovoltaic properties of ZnO nanowire array films

Single-crystalline ZnO nanowire arrays with different aspect ratios and nanowire densities were prepared by the hydrothermal growing method using polyethyleneimine (PEI) as a surfactant. PEI can only hinder the lateral growth of the ZnO nanowires, which is observed by high resolution transmission electron microscopy (HRTEM) analysis. Dye-sensitized solar cells were assembled by the ZnO nanowire arrays with different thicknesses, which can be controlled by the growing time and characterized using photocurrent-voltage measurements. Their photocurrent densities and energy allover conversion efficiencies increased with increasing ZnO nanowire lengths. Short-circuit current den-sity of 4.31 mA-cm-2 and allover energy conversion efficiency of 0.87% were achieved with 12.9-μm-long ZnO nanowire arrays.     

α-Ni(OH)2 electrodeposition from NiCl2 solution

α-Ni(OH)₂ was synthesized from a NiCl₂ solution by electrodeposition method. In order to conduct a systematic study on the effects of experimental parameters, a series of electrolyte initial pH values, current densities, electrodeposition temperatures, and electrodeposition time were used. Cyclic voltammetry results demonstrated a side reaction of Ni²⁺+2e→Ni. The X-ray diffraction analysis, Fourier-transform infrared spectrum, and the color of the product showed that pure α-Ni(OH)₂ could be obtained in the initial pH value range of 2–5.86, current density range of 10–25 mA/cm² electrodeposition temperature range of 25–35 °C, and electrodeposition time range of 1.0–3.0 h. When electrodeposition temperature increased to 45 °C, a mixture of α-Ni(OH)₂ and metallic Ni was obtained. A current density higher than 30 mA/cm² resulted in the sample with features of β-Ni(OH)₂. A small amount of metallic Ni existed in the as-prepared sample when current density decreased to 5 mA/cm². A slight increase of electrolyte pH was observed with increasing initial solution pH and current density. Electrodeposition mass revealed a slight decrease with initial pH decreasing and showed an almost linear increase with current density increasing. The slope of the curve for electrodeposition mass versus electrodeposition time remained stable in the first 2.0 h and then decreased.     

Mathematical modeling of electrodeposition of permalloy thin film I. direct current plating

A mathematical model is presented to describe the electrodeposition of Ni-Fe alloy film on a rotating disk electrode in chloride solution. The model incorporated with anomalous codeposition phenomena agrees well with the experimental data under a variety of conditions. The Fe content in permalloy shows a maximum at current densities between 2 mA/cm² and 5 mA/cm², then decreases monotonically as a function of the applied current density. Also experimental and simulated results are discussed in terms of solution pH, rotating disk speed, and iron concentration which affects the Fe content in the permalloy during electrodeposition.     

Corrosion inhibition performance of polymer-alloy bilayer coatings: electropolymerised polyaniline and electrodeposited ZnNi with different layer orders

Polyaniline (PANI) conducting polymer coatings have been obtained galvanostatically with various current densities (from 0·1 to 0·4 mA cm^?2) and ZnNi alloy coatings have been obtained galvanostatically at 30 mA cm^?2 current density. Corrosion protection performances of monolayered PANI and ZnNi alloy coatings and multi-layered ZnNi/PANI and PANI/ZnNi coatings on st-37 low carbon mild steel (MS) have been investigated by an open circuit potential method, Tafel extrapolation method and electrochemical impedance method in 3·5 wt-% NaCl solution. In addition, the surface morphology of the coatings has been characterised by using scanning electron microscopy (SEM). Synthesising PANI films between two metal layers provided better corrosion protection to the steel. MS/PANI/ZnNi layer formation exhibited the biggest corrosion protection performance among all layer formations of the films and protected MS for up to 72 h.     

Enhanced ferroelectric, dielectric and optical behavior in Li-doped ZnO nanorods

Enhancement in the dielectric and ferroelectric properties has been observed in case of Li-doped ZnO nanorods (NR). Effect of Li-doping on ZnO structure and its optical properties has also been reported. In high resolution TEM studies, the length and diameter of as-synthesized Li-ZnO nanorods were found in the range of 100-150 nm and 20-70 nm, respectively. XRD studies, Li-doped ZnO NR exhibited wurzite structure in which lattice parameter becomes larger than the pure ZnO NR. In dielectric studies, higher dielectric constant and a ferroelectric phase transition at 72 °C were observed. In ferroelectric studies, high remnant polarization of 0.873 μC/cm² and low coercive field of 0.592 kV/cm were observed, which were better than their values in bulk Li-doped ZnO (0.044 μC/cm² and 2.0 kV/cm, respectively). In UV-Vis spectra, low absorption band edge at 352 nm was observed due to the size effect in the ZnO nanorods. In addition, PL spectra show a blue shift in both UV and visible region as a result of doping. These results are discussed in the light of the nanorods of confined geometry.     

The mechanism of caustic cracking of carbon steels—I. Influence of electrode potential and film formation

The anodic behaviour of a 0·1% carbon steel wire in 10M sodium hydroxide solution at 121°C has been studied at different electrode potentials under static conditions, and while the wire yields at strain rates between 1·5 and 436%/min.The static material forms a fairly coherent and adherent film of magnetite in the potential range ca. ?0·60 to ?0·85 V(she), while the anodic current density falls to ca. 0·2 mA/cm² (at ?0·70 V) in ca. 40 min. When such a specimen is made to yield at 436%/min, the overall current density continuously rises to over 8 mA/cm² at the bared metal area produced by the cracking of the oxide film. This current density is sufficient to account for the rate of crack propagation measured microscopically on specimens strained at 1·5%/min. Equivalent results are reported for potentials over the whole range ?0·60 to ?0·85 V(she).On either side of this potential range little or no adherent film is formed, the anodic current density does not fall below ca. 1 mA/cm² and on straining rises to no more than ca. 5 mA/cm²; and no cracks are produced.The results strongly support the theory that crack propagation occurs because bared metal at the yielding advancing edge of a stress-raising crack can dissolve several hundred times as fast as that at the static crack sides, which are continuously protected by the growth of film. The crack thus maintains its acuity, and the raised stress at its edge maintains ductile yielding of the metal so that the electrochemical crack advancement proceeds without the need for any mechanical cracking.A comparison with previously reported work on the same steel in hot concentrated nitrate solutions shows that the range of anodic current densities found on bared metal, and the corresponding range of crack propagation rates, are about an order of magnitude less in the present hot concentrated hydroxide solution.     

Morphological investigations of polypyrrole coatings on stainless steel

In this paper, electrochemical polymerization of pyrrole on 316L stainless steel substrates was accomplished using a rotating disc electrode (RDE). By applying various current densities and disc rotation speeds, coatings were produced with the aid of galvanostatic technique. Experiments were performed in an aqueous solution containing 0.2 M pyrrole and 0.1 M oxalic acid. Current densities and disc rotation speed ranges were from 0.05 to 1.0 mA/cm² and from 0 to 1500 rpm, respectively. Using a scanning electron microscope (SEM), the morphology of polypyrrole coatings was studied, and the morphology diagram was determined. The results obtained showed that various morphologies were obtained by changing the current density and/or disc rotation speed. These results also showed that apart from conventional morphologies of polypyrrole coatings reported in the literature, a new semicrystalline morphology was obtained under the conditions of very low current density (0.05 mA/cm²) and disc rotation speed (≤50 rpm). The degree of crystallinity of this morphology was estimated to be 68% by grazing-incidence small-angle X-ray scattering (GISAXS). The elemental analysis (CHN) revealed the ratio of semicrystalline polypyrrole to oxalic acid dopant to be 4:1.     

电流密度对ZK60镁合金表面超疏水涂层的制备及耐腐蚀性的影响

为了提高镁合金的耐腐蚀性能,基于层状双氢氧化物（LDHs）膜在ZK60镁合金表面制备了超疏水（SH）涂层。涂层制备过程中引入电场辅助,研究了工作电流密度对涂层性能的影响。结果表明,工作电流密度显著影响LDHs膜的微观结构,这对SH涂层的疏水性具有重要影响。当工作电流密度为25 mA/cm²时,SH涂层表面呈现均匀的微纳米结构,并表现出超疏水性。超疏水涂层的腐蚀电流密度（I_corr=9×10^-7 A·cm^-2）比ZK60基体的腐蚀电流密度（I_corr=3×10^-5 A·cm^-2）低了2个数量级,表现出优异的耐腐蚀性。     

Morphology of alpha-lead dioxide electrodeposited on aluminum substrate electrode

Alpha-lead dioxide was deposited by anodization of alkaline solution containing HPbO2- anions. Scanning electron microscopy (SEM) results show that the morphology is remarkably affected by the current density, concentration of HPbO2- anions, bath temperature and electroplating time. Compact and well adherent layers are possibly obtained under conditions of current densities ≤3 mA/cm2, electrolyte containing 4 mol/L NaOH and 0.12-0.14 mol/L lead (Ⅱ ), bath temperature of 40 ℃, and electroplating time of 2 h. EDS analyses show that the PbO2 deposited in alkaline condition is highly non-stoichiometric at high current density.     

The electrochemical deposition of Zn–Mn coating from choline chloride–urea deep eutectic solvent

Electrochemical and microscopic techniques were used for the characterisation of Zn–Mn coatings electrodeposited from choline chloride–urea deep eutectic solvent. Cyclic voltammograms show that there was no discernible Mn reduction peak when only Mn²⁺ was present in DES solution. The distinct Mn peak developed only upon addition of Zn²⁺ to the solution, probably due to previous Zn nucleation on the steel substrate. It was found that 22–27?wt-% Mn deposited at current densities of 3–8?mA?cm^?2, amounts significantly higher than those obtained from aqueous electrolytes. Since higher deposition current densities resulted in the formation of a porous surface consisting of clusters of nodular crystallites, the optimal deposition c.d was determined to be 3?mA?cm^?2.     

氢化TiO2纳米棒的制备及其对Q235碳钢的光生阴极保护特性

随着海洋开发的逐步推进,海洋工程中的金属防腐蚀问题显得愈加重要。目前,可利用半导体的光电效应实现对金属的光生阴极保护,为改善常用的TiO₂光电极材料的弱光吸收和低转换效率问题,文中利用水热法在FTO导电玻璃表面构建一维有序TiO₂纳米棒阵列,并通过氢化处理提高TiO₂对太阳光的吸收和光电流密度。考察了氢化TiO₂纳米棒阵列在海水环境下对Q235碳钢的光生阴极保护特性,结果表明氢化TiO₂纳米棒的光电流密度达到了2.12 mA/cm²,且稳定性良好;当Q235碳钢耦连于模拟太阳光照下的氢化TiO₂纳米棒电极时,其界面反应电阻变小,电极电位较原先的腐蚀电位降低约349 mV,说明氢化TiO₂纳米棒阵列能够对碳钢产生良好的光生阴极保护效应,且该效应在无光条件下能保持至少7 h。