Dissolution patterning of thin sputter-deposited Al film formed on glass plate was examined by bringing a cathodically polarized small electrode near it. Hydrogen gas evolution on the small electrode causes enough alkalization of electrolyte solution around the electrode to dissolve Al film due to its amphoteric nature. A dissolution pattern less than 1mm in size with a dissolution width of ca. 0.1mm was obtained using a cathodically polarized thin Cu wire electrode brought near to the Al film surface and scanned along the surface.

View full abstract

Hydantoin derivatives were investigated as the complexing agents for gold plating. 1-Methylhydantoin (MH), 5,5-dimethylhydantoin (DMH) and 1,5,5-trimethylhydantoin (TMH) were tested. HAuCl₄ was used as the gold source and phosphate salt was contained as the pH buffer. Thallium ion was added to refine the deposited grains. These complexing agents shifted the deposition potential to a less noble side, which suggested that these agents had a function of stabilizing the gold complex. The process with DMH and TMH deposits a uniform and dense film. The deposition efficiency of the bath containing DMH and TMH was approximately 40.8 mg/A·min, which is 100% of the current efficiency for the trivalent state of gold, while that for the bath with MH was even larger. From the result of measuring the limiting current using a rotating disc electrode, the number of electrons transferred for the plating in the MH bath was conspicuously smaller than that of the DMH bath. Therefore, it was suggested that a monovalent gold complex was formed in the MH bath.

View full abstract

The effect of electrolysis conditions on the self-ordering of the cell arrangement of anodic porous alumina grown in malonic acid solution was investigated for the clarification of the mechanism. Because the cell arrangement of porous alumina is affected by the roughness of the substrate surface, the aluminum substrates were pre-treated by electropolishing followed by chemical polishing to modify the substrate surface and make it suitable for uniform porous film growth. By lowering the electrolyte temperature, the high voltage anodizing accompanying high current density without appearance of local current concentration, i.e., burning, could be archived to obtain self-organized porous alumina. Further, current density could be increased more by increasing malonic acid concentration. The porosity of anodic alumina formed in malonic acid solution was 0.07, regardless of the anodizing voltage. From the above results, it was confirmed that high current density, i.e., high electric field strength is the key controlling factor in the self-ordering of anodic porous alumina.

View full abstract

Niobium specimens with chemical polishing were anodized in a phosphoric acid solution galvanostatically at i_a,ini=1, 10, 100 and 1000Am⁻² up to E_a=100V, and then potentiostatically at E_a=100V for t_pa=7.2ks. During galvanostatic anodizing, the anode potential increased almost linearly with time on all the specimens, while, during potentiostatic anodizing, the anodic current decreased with time. The current density at t_pa=7.2ks was higher at lower i_a,ini in the range of 0.02 to 0.25Am⁻². The spectra of Rutherford backscattering spectroscopy (RBS) and glow discharge optical emission spectroscopy (GD-OES) showed that higher i_a,ini causes film thickness to decrease and the amount of incorporated phosphorus to increase. Micro imperfections were formed in the film at the ridge of the convex network structure produced by chemical polishing, and the number of imperfections decreased with increasing i_a,ini. Parallel equivalent capacitance, C_p, and the dielectric dissipation factor, tan δ, of anodic oxide films decreased with increasing i_a,ini. The mechanism of decrease in the number of imperfections in anodic oxide with increasing i_a,ini is discussed in term of film thickness, phosphorus incorporation and Nb⁵⁺ transport number.

View full abstract

The anodizing behavior and crystallization of anodic oxide films formed on niobium in sulfuric acid were investigated by measurement of current density transient during voltage holding, voltage-time curves on re-anodizing, leakage current, capacitance and X-ray diffraction, and by observation of film structure at different stages. Current density transient during voltage holding, which was reflected in crystallization of anodic niobium oxide films, was divided into three regions : first current decay region (nucleation of crystalline oxide), current increasing region (development of crystallization), and second current decay region (repair of defects in the film). From the detailed observation of the fracture sections of oxide films by SEM, it was confirmed that the crystallization occurred during first current decay region. The features of the cracks, which were produced by volume expansion of crystalline oxide particles forming within the amorphous oxide layer, were quite similar to those associated with tantalum oxide films. With increasing anodizing time, the crystalline areas grew outwards radially, pushing up the amorphous film like petals. The available experimental data on various electrochemical measurements was in good agreement with the directly observed transformation of crystalline areas in the oxide film during anodizing. The crystallization of the film during anodizing of niobium was accelerated by employing a low acid concentration at high temperature and high anodizing voltage. The dielectric properties of the crystallized film deteriorated except for capacitance, in comparison with the amorphous film formed on niobium.

View full abstract