We prepared transparent and hard silicon oxide films having water-repellent surfaces. In the multiple-step microwave plasma-enhanced chemical vapor deposition (MW PECVD) we developed, silicon oxide layer was prepared using mixture of tetrametylsilane (TMS) or tetramethoxysilane (TMOS) and oxygen (O2) as source gases. Next, O2 was exchanged to FAS-17 ((heptadecafluoro-1, 1, 2, 2, tetrahydro-decyl)-1-trimethoxysilane). We introduced FAS-17/Ar into the reactor using Ar as the carrier gas. The O2 supply decreased gradually, then was depleted. Al-10min water-repellent layer was deposited after TMS or TMOS partial pressure was adjusted to equal that of FAS-17/Ar. The contact angles obtained depend strongly on organosilicon compounds and substrate temperatures. Silicon oxide film surfaces treated with TMS without methoxy groups and FAS-17/Ar at 70°C had high water-contact angle of 120 degrees. The water repellency of films obtained by multistep CVD was inferior to that of single layers of water-repellent films prepared from TMS and FAS-17/Ar without O2 in the first step of film preparation. Residual oxygen in the reactor oxidized the water-repellent layer, reducing the hydrophobic properties of the surface. The ultramicrohardness of the silicon oxide films having water-repellent surfaces depended on the thickness of the water-repellent layer. The carbon concentration of films obtained in the multistep CVD gradually decreased from the surfaces to the insides, i. e., surfaces showed an organic nature even though inner regions were inorganic.
SUS 304 stainless steel plate was dipped in molten Al-Si alloy laving different Si concentrations, i.e., hypoeutectic, eutectic, and hypereutectic. The effect of Si concentration on coating layer formation was studied by metallographic observation and EPMA analysis. Diffusion heat treatment of hot-dipped samples was also conducted and the change in the coating layer structure examined. Metallographic examination showed that the adhered layers of samples hot-dipped in hypoeutectic and eutectic Al-Si alloy baths are the same as the solidified structures of conventionally cast Al-Si Alloys. The CrSi2-Alx phase was observed in the adhered coating layer of the sample hot-dipped in hypereutectic alloy. The amount of CrAl2-Alx increased with increasing bath temperature and immersion time. Fe-Al-Cr-Si alloy layers formed at the interface of the stainless steel and molten alloy, and grew to a maximum thickness of about 20μm. The alloy layer growth rate and maximum thickness did not depend on Si concentration in the Al-Si alloy bath.
High concentrations of cyanide and alkali in baths had the objective of lowering whisker growth in zinc plating, but the mechanism and suitable bath composition remain to be clarified. We studied chemical species concentrations, taking the ion balance into consideration, and found that the carbon content in zinc plating, and the amount of zinc cyanide complexes and free cyanide ions in baths are related to whisker growth. Zincate ions are related to the electrodeposition rate but not to whisker growth. The ratio of zincate ion to zinc cyanide complexes in the cyanide system we studied, is closer to the work of Hasko and Kunkel indicated in the standard cyanide system [Zn(OH)42-]:[Zn(CN)42-]≅1:1; in the highcyanide system [Zn(OH)42-]:[ZnCN]42-]≅1:2-3) than to the work of Hull and Wernlund indicated (75 to 90% of zinc in the standard cyanide system was present as zincate ion and the remainder as zinc cyanide complexes). This concentration of chemical species can be used as an index of zinc plating baths control instead of ratio M (NaCN/Zn).
A Ni suicide layer on Ni substrate was formed by electrodepositing Si and alloying it with Ni in molten salt. Electrolysis was conducted using potentiostatic polarization at constant potentials in an equimolar NaCl-KCl melt containing 5mol% K2SiF6 at 1023K. The maximum mass of electrodeposited material was obtained at -1.3V (vs. Ag/Ag+(0.1)). Deposits formed at -1.2 to -1.5V were conical or cylindrical surface crystals and film-like material beneath crystals. Such deposits consist of Ni silicides such as α-NiSi2, NiSi and ε-Ni3Si2. Si content in deposits decreased with increasing depth from the surface to the deposit/substrate interface. Nickel covered by the electrodeposit was more resistant than bare nickel to hot corrosion by molten Na2SO4.
Migration is the short-circuiting between electrodes on printed circuit boards, often observed in the presence of moisture, that reduces electronics reliability. Migration has been assumed to be due to anodic dissolution and cathodic deposition, but quantitative and in situ monitoring of the process is difficult. We used a quartz crystal microbalance (QCM) to study migration, and found that anodic dissolution and cathodic deposition increase over time until short-circuiting occurs, but surpressed thereafter.
TEM and ESCA observations have been used to study copper crystallite sizes, tin and oxygen atom concentration distributions, tin oxidation, and the crystal structure of tin oxide, compared to electrolytic polycrystalline copper deposits with no impurity atoms (pure copper deposits). The 0.003wt%Sn-Cu alloy deposited in a copper electrolyte containing a tin additive of 1g/dm3 showed almost the same results as the pure copper deposit. For the 1.10wt%Sn-Cu alloy produced in an electrolyte containing a tin additive of 10g/dm3, tin atoms were found to be incorporated into copper deposits in both metallic and oxidation states. Tin oxide particles (SnO2) having a rutile (or C4) tetragonal structure were observed to be a smooth and elliptical, 2-5nm in size, and almost homogeneously dispersed as clusters of several particles inside copper deposits. We also sound in nm-order SnO2 particle incorporation that particles form in the copper electrolyte and are concomitantly introduced into copper deposits during alloy electrodeposition.
Dispersed TiO2 particles form an adsorption equilibrium on the surface of a cathode in the electrolyte. Equilibrium is strongly affected by the surfactant concentration, which is related to the zeta potential of dispersed TiO2 particles. Particles having a large zeta potential disperse stably without aggregation, because the repulsive force between particles is large. Particles having a small zeta potential aggregate and produce rough particles, decreasing the number of particles, that collide with and are adsorbed on the cathode. Rough particles easily desorbed from the cathode because of their weight, decreasing the amount of codeposited particles.