As a main optical thin-film material, SiO₂ has a low refractive index in the UV-visible wavelength region. It is used widely for optical coatings with superior environmental resistance. In contrast, Nb₂O₅ is a high refractive index material. To improve their mechanical properties, SiO₂ and Nb₂O₅ single-layer thin films were prepared using high-density plasma assisted vapor deposition. Plasma conditions were varied by changing the coil current related to energy intensity, and the oxygen gas flow rate related to ionization. Analyses of SiO₂ and Nb₂O₅ thin films using XRD revealed amorphous composition irrespective of the assist. However, cross-sectional SEM images showed that thin film densification differed according to the assist. Furthermore, XPS showed differences in SiO₂ thin films from the bonding state according to the assist. The Nb₂O₅ thin films exhibited slight differences according to the assist. Surface roughness measurements and abrasion resistance tests were done for thin films deposited under various plasma conditions. The plasma-assisted deposited SiO₂ films were much more durable than non-assist films. The refractive indexes of the films were measured using optical transmission spectra and ellipsometry. Results show correlation between the durability and the refractive indexes. The film packing density was related to the durability. No difference was found in the durability for Nb₂O₅ between plasma-assisted deposited films and non-assisted deposited ones. However, a difference was found in the refractive index between the films of two types. The film hardness was measured using nanoindentation. The Nb₂O₅ films were harder than the SiO₂ films. The Nb₂O₅ film stiffness was also three times greater than that of SiO₂ films. However, the damage to plasma-assisted SiO₂ films was less than that to plasma-assisted Nb₂O₅ films. This high stiffness is expected to cause plastic deformation. Future investigations must examine the relations among film packing density, durability, hardness, and stiffness.

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Carbon nitride, which has fascinating properties such as high hardness and high current density of field emission, was investigated to elucidate the tribological properties of carbon nitride synthesized using microwave plasma CVD against CVD diamond. Carbon nitride was synthesized using microwave plasma CVD with a mixture of CH₄-N₂ gas used as a reaction gas. The CH₄ flow rate was varied from 1 to 3 SCCM. Using a ball-on-disk friction tester, tribological properties of the deposits were estimated. Counterpart materials were CVD diamond film coated onto the SiC ball using microwave plasma CVD. Regarding the estimation of tribological properties, the lowest coefficient of about 0.05 against diamond was obtained for deposits made with a CH₄ flow rate 2 SCCM. The wear depth was shallow against deposits synthesized in a CH₄ flow rate of 2 SCCM. Results demonstrate that tribological properties of carbon nitride against diamond had a low friction coefficient. Deposits synthesized in a CH₄ flow rate of 2 SCCM exhibited the shallowest wear depth.

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To clarify the effects of collision of small glass particles of FePO₄ or glass on the corrosion rate of iron, mass losses of iron after immersion in a glass and Na₃PO₄ solution at 343 K were measured under a shaking condition. Mass losses in solutions containing the particles were twice as high as in a solution without the particles. Results show that particle collision with specimens enhances corrosion.

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