The storage density of hard disk drives is increasing significantly by a technique applied to the Al-alloy disk substrate to reduce defects in the electroless Ni-P plating layer. Because of recent increases in storage density, ultrasmall（less than 1 lm）pinholes in the Ni-P plating layer have become an important difficulty. Various mechanisms for the initiation of the ultrasmall pinholes have been investigated, but these mechanisms are not based on experimentally obtained data. The ultrasmall defect size makes it extremely difficult to ascertain their overall appearance. For this study, we applied scanning transmission electron microscope-energy dispersive x-ray spectroscopy to analyze an ultrasmall pinhole. Based on detailed analysis, we obtained an overall defect image suggesting that the ultrasmall pinholes are paths formed by migration of Al^3＋ generated by the dissolution reaction of the Al substrate（Al→Al^3＋＋3e⁻）during the electroless plating process.

Effects of sulfate on film structure and formation behavior during plasma electrolytic oxidation（PEO） of titanium were investigated. PEO was conducted at a constant current density of 200 Am⁻² in aqueous sodium phosphate solutions. When magnesium sulfate was added to the electrolyte, the breakdown voltage during PEO decreased along with increasing amounts of magnesium sulfate. The obtained PEO coating was white, different from the grayish color of the film formed in sodium phosphate solutions without magnesium sulfate. Compositional analysis results showed that Na, P, Mg, S, and O（derived from the electrolyte） and Ti（derived from the substrate） were contained in the coating. The electrolyte composition and concentration play a crucially important role in the PEO coating composition and structure. Furthermore, XRD patterns showed that the coating mainly comprised rutile phase. The findings of this study are expected to facilitate new applications for composite materials based on titanium dioxide and sulfate.

For boron-doped diamond films synthesized using the hot filament CVD method, their oxidation resistance mechanisms were investigated. Heating the films in air has demonstrated that boron addition reduces the diamond film oxidation rate. Moreover, B₂O₃ was detected on the etched surfaces of the boron-doped diamond films. The B₂O₃ presumably serves as a protective film to suppress oxidation of the boron-doped diamond, leading to high chemical wear resistance of boron-doped diamond.