Yttrium oxide, Y₂O₃, was deposited on a Si (001) substrate in ultrahigh vacuum by the simultaneous irradiation of arc plasma of yttrium and hyperthermal atomic oxygen, the principles and procedures of which were introduced in the preceding article. X-ray photoelectron spectroscopy revealed that the stoichiometry of Y₂O₃ was identical from the top to the bottom of the film. Y₂O₃ film deposited at a substrate temperature of 300℃, followed by a post-annealing process at 700℃, showed a low friction coefficient of approximately 0.1. At ＋high deposition temperatures, e.g. 500℃ and 700℃, faint Si2p peak was detected at an early stage of Ar depth profiling. Presumably, this may lead to inferior film properties. Low friction as well as good adhesion property of Y₂O₃ film to the Si(001) seems applicable to protective coating of MEMS (microelectromechanical systems) and other Si technologies.

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Ultra-thin optical interferometry revealed that grease formed thick elastohydrodynamic lubrication (EHL) films at extremely low speeds, 2mm/s for example, demonstrating a V-shaped film-thickness-vs.-speed plot, as previously reported. The present work tries to confirm that this characteristic behavior occurs in ball bearings. A pair of deep-groove ball bearings (6204) were run at 1-600 rpm under an axial load of 400 N, lubricated with greases and also with their base oils. The electrical potential across the ball-groove interfaces was measured in order to monitor the formation of an EHL film, and friction torque was monitored simultaneously. When lubricated with grease, the electrical potential behavior at higher speeds was similar to that measured with the base oil alone, but at low speeds it displayed a marked difference, by virtue of the formation of thick EHL films in the ball bearings, which also contributed to reducing the frictional torque.

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