2016 Volume 67 Issue 6 Pages 322-327
For this study, we prepared CF4 plasma treated and untreated diamond films. Untreated smooth diamond films were prepared by polishing after deposition. Then CF4 plasma treated diamond films were produced using fluorocarbon plasma treatment. The diamond peak intensity in the Raman spectra of diamond film decreased, whereas that of graphitic peaks increased during fluorocarbon plasma treatment. Results show that the treatment increased the water contact angle of the film and decreased its surface energy. Atomic force microscopy measurements revealed remarkably lower surface roughness in high humidity conditions. In addition, CF4 plasma treated diamond film showed remarkably lower nanofriction than that of untreated diamond film. The boundary lubrication properties of untreated and CF4 plasma treated diamond films were examined with various water solutions. The diamond film friction coefficients were low: less than 0.07 under boundary lubrication with water. The diamond film friction coefficient when lubricated with tap water was lower than when lubricated with distilled water. To clarify the reasons underlying this difference, the tap water was electrolyzed into ion water. The friction coefficient of untreated diamond films lubricated with acid ion water was lower than that with alkali ion water because of the presence of negative ions. The friction coefficient of untreated diamond film lubricated with 0.85% salt solution was low. Moreover, the friction coefficient when lubricated with dilute hydrochloric acid（HCl）was low. It was equal to that observed for physiological saline solution. For the untreated diamond film, Cl－ ions contributed to the friction reduction.
