We investigated the photoanodic polarization behavior of TiO2 films formed on TiN and Ti2N by high-temperature oxidation under pressures from 1.01×101 to 1.01×105 Pa O2 in a Na2SO4 solution. TiO2 films formed on TiN and Ti2N and a TiO2 film formed on metallic titanium were rutile with no nitrogen detected. Photo-anodic currents of TiO2 films on TiN, Ti2N, and metallic titanium increased, in that order. The current of the TiO2 on TiN film was especially large. However, the energy bandgaps of the TiO2 films were not substrate-dependent. The reason for the large current of the TiO2 on TiN film is considered from the result of nonstoichiometric composition of the TiO2 film surface that developed during the TiO2 film growth process.
Exposure time effect on solder-joint pull between a substrate and a copper bump at 150°C was studied. Copper bumps formed in a copper sulfate plating bath are well known to be reliable in semiconductor electrode applications, but are still being studied for applications in the automotive industry. SEM confirmed that voids caused by Cu-Sn diffusion grew at the interface between the copper layer and Cu-Sn alloy layer after durability testing at 150°C. EPMA showed that sulphur segregation occurred near the void and that voids grew in proportion to the sulphur concentration. Small amounts of sulphur remaining in copper bumps are thought to diffuse with vacancies at the interface and promote void growth. To improve reliability, sulphur concentration at copper bumps should be suppressed during copper sulfate plating.
Membrane potentials of α-Ni(OH)2 and β-NiOOH electrochemically prepared on Pt mesh, were measured in neutral aqueous solutions of KCl, KNO3, NaCl and Na2SO4 at 25°C to determine the transport number of electrolyte ions in nickel hydroxide and oxy-hydroxide. The anion transport number, (t_=0.99-0.93), in α-Ni(OH)2 was larger than that(t_=0.62-0.49) in the bulk solutions, indicating that α-Ni(OH)2 has high selective anion permeability. On the other hand, the anion transport number, (t_=0.64-0.51), in β-NiOOH was not significantly different from that in the bulk solutions, indicating that β-NiOOH has low selective anion permeability. This low selective anion permeability may be attributed to the low positive fixed charge density of β-NiOOH in the measured solutions.
Electroless displacement plating of silver on copper plate in a high magnetic field was studied in controlled experiments without a magnetic field gradient or gravity convection at a constant temperature. Plating silver weight decreased quickly up to 1T as magnetic flux density increased. From 1T to 10T, plating silver weight increased gradually with magnetic flux density. The morphology of the plating surface showed heterogeneous deposition as silver weight decreased.