The self-organizing abilities of molecular and nano-sized systems have been explored to form ordered nano-sized structures. Some germinant unique examples of such nano-structures, produced by chemical and electrochemical methods, are reviewed. The first example is formation of nano-holes at atomically flat, H-terminated n-Si (111) surfaces, which occurs during electrochemical deposition of Pt. Reductive dissolution of the Si surface, catalyzed by Pt in a mono-atomic state as a reaction intermediate of the Pt deposition, is proposed as a plausible mechanism. The second example is formation of ordered iodine nano-rods on atomically flat, H-terminated n-Si (111) surfaces, which occurs upon their immersion in 7.1 M HI. The formation of iodine nano-rods was closely related with that of Si-iodine termination bonds. The third example is formation of ordered arrays of gold nano-particles in aqueous solutions and on gold (111) surfaces, which occurs by addition of organic thiols to particle solutions. The aspect ratio of the ordered arrays depended on the kind of thiols added. These examples strongly suggest that the chemical and electrochemical methods are a promising approach to production of ordered nano-structures on solid surfaces.
A novel electrochemical disinfecting cell was developed in which the electrodialysis and ion-exchange resins were combined and offered to the inactivation of bacteriophage. The cell was composed of 6 compartments and either side of the center compartment was partitioned by two similar ion-exchange membranes. In addition, the compartment was stuffed with the same type of the ion-exchange resins as the ion-exchange membranes, i.e. the anion-exchange resins for the anion-exchange membrane compartment (A || A) and the cation-exchange resins for the cation-exchange membrane compartment (C || C). The characteristic feature of the cell was that the salt concentration was kept constant either in the C || C or in the A || A compartments. Only inactivation effect due to the current flow can be revealed in such compartments and the effect of either the electrode materials or the electrolytic products was completely avoided. The significant inactivation of bacteriophage was observed in the A || A compartment in which OH− or Cl− type ion-exchange resins were stuffed. The inactivation effect in the C || C compartment was hardly observed. According to the finding, the inactivation in the A || A compartment was found to occur due to the current flow through the body of bacteriophage itself.
Electroless copper deposition on the wall of the blind via holes was numerically simulated by solving a conventional diffusion equation with the reduction reaction of copper (II) on the wall. Highly non-uniform copper deposition was ascribed to the small rate of copper (II) transport to the inmost part of the hole in comparison with the rate of the copper deposition, particularly in the cases of the aspect ratios of two or greater. According to the preliminary runs of the copper deposition, an application of the ultrasonic vibration at the deposition step improved the uniformity substantially but not very significantly. Having been expected the enhanced transfer of copper (II) in the hole, temperature gradient along the axis of the hole was applied in the simulation of the copper deposition, which results suggested more uniform copper deposition than in the isothermal condition. Experimentally, copper deposited preferentially rather at the inmost part of the hole under the conditions of 298 K at the hole opening and 338 K at the bottom. It was found that the temperature gradient copper deposition on the wall of the blind via holes provides us with the uniform layer of copper.
Anodic oxidation of single crystalline silicon was carried out in constant current and constant voltage modes using a solution of 0.04 N HNO3 in an ethylene glycol at temperatures of 20 to 70°C. The current and voltage between an anode and a cathode were measured during the anodic oxidation process. The influence of anodic oxidation temperature on the growth process of silicon dioxide films was studied by current-time characteristics. The silicon dioxide films grown on silicon wafers were analyzed by XPS to study the influence of the electrolyte temperature and hydroxides content. The transition time when the voltage between the anode and cathode reaches the preset-up voltage had a maximum value at 45°C. The silicon dioxide film thickness and capacitance had a maximum and minimum, respectively, when the anodization was carried out at 45°C. Stoichiometric SiO2 films could not be formed at this temperature. The XPS peak intensities of Si4+ and Si0+ in anodically oxidized films depended on the electrolyte temperature. The Si4+ peak appeared even in the substrate for the films anodized at 45°C. It was confirmed that the boundary region existed between the SiO2 film and Si substrate. Furthermore, hydroxides existing within the film was concentrated at the silicon dioxide-silicon boundary at 45°C. The property of oxide films depends on the content of hydroxide, which is a function of the anodization temperature.
Examination was made of metal ion elution from eight different dental alloys in the artificial saliva solution with Compound iodine glycerin by voltammetry, potentiometry, specular reflection and atomic absorption spectrometry. The rest potential of anyone of these dental alloys in the artificial saliva solution containing 2.0% Compound iodine glycerin was more positive than in the artificial saliva solution alone. The amount of eluted Cu ions from the gold-based alloy and that of eluted Ni ions from the Ni-Cr alloy increased with Compound iodine glycerin concentration. The amount of eluted metal ions from alloys containing Cr was very small due to passive film formation and the more positive rest potential of alloys containing many Cr than an alloy with less Cr.
Electrochemical behavior of polyaniline coated spinel LiMn2O4 has been studied to improve the cycling performance of LiMn2O4 at 50°C. The polyaniline coated LiMn2O4 electrode shows more excellent cycling performance than polyaniline-LiMn2O4 mixture electrode, in which the capacity of LiMn2O4 decreases and that of polyaniline keeps constant value during the cycling. This result indicates polyaniline coating for LiMn2O4 is effective to improve the cycling performance of LiMn2O4. Further, 5 wt% polyaniline coating is enough high to improve the cycling performance. This would be due to the coverage of spinel LiMn2O4 with polyaniline, which protects the dissolution of manganese by separating spinel LiMn2O4 from the electrolyte. It is also confirmed that polyaniline itself shows excellent cycling performance in 4 V region.
Lanthanum was electrodeposited on a Ni substrate in molten chlorides and the alloying treatment between the electrodeposit and the Ni substrate was carried out to obtain hydrogen absorption alloy film such as LaNi5. The change of open-circuit potential of the Ni substrate during the alloying process was also measured after the electrolysis in the molten salts. It was found that the potential shifted to noble direction with time and several potentials showing constant values for a while were observed at −1.88 V, −1.76 V, −1.45 V and −0.50 V until reaching the rest potential of the Ni substrate, −0.27 V. The specimens were picked up at these various plateau potentials, cooled rapidly and subjected to the X-ray diffraction analysis, the EPMA line analysis and SEM observation to identify the alloy phase formed at each potential. These constant potentials corresponded to the equilibrium potentials between two phases consisting of La-Ni alloys or Ni substrate on the surface. The relationships between these potentials and the alloy on the surface were considered from these results.
The method to determine an instantaneous impedance was developed for the impedance without time stability. The Nyquist plot of the impedance without time stability shows the deviation from the semicircle in the low frequency range. In the present method, the impedance was measured four times successively. The measured impedance spectra were plotted on 3-D Nyquist plane, whose axes were real and imaginary components and time. The data was joined by a smooth curve at the same frequency using spline function. The instantaneous impedance can be determined by the cross section of 3-D Nyquist plot. The program of this compensation was described, and this method was applied to the impedance of iron electrode which showed inductive loop.