Makoto Kitoh

Influence of exposure to an atmosphere of high relative humidity on tribological properties of diamondlike carbon films

‘‘Diamondlike’’ carbon films have potential applications because of their high wear resistances. We have investigated the influence of exposure to an atmosphere of high relative humidity (RH) on tribological properties of carbon films prepared with a radio‐frequency plasma enhanced chemical vapor deposition. Wear characteristics were measured using a pin‐on‐disk wear tester. A friction coefficient of a carbon film as deposited was as low as 0.2. However, the value increased up to 0.3–0.4 after exposure to an atmosphere of 60 °C 90% RH for seven days. Electron spectroscopy for chemical analysis and electron energy‐loss spectroscopy analysis suggested that a very thin (<1 nm) unstable surface layer of the film had suffered a chemical change during the exposure process. We have found that the change can be suppressed by increasing a degree of fragmentation of the hydrocarbon source in the plasma, or by removing the unstable layer with an Ar plasma etching.

STRUCTURAL ANALYSIS OF HYDROGENATED CARBON FILMS OBTAINED BY REACTIVE DIRECT CURRENT MAGNETRON SPUTTERING

Amorphous hydrogenated carbon films were prepared by reactive direct current magnetron sputtering in argon plasma containing methane as the reactant gas. The films were characterized using various spectroscopic measurements such as Raman scattering, optical absorption spectroscopy in the ultraviolet–visible region, and infrared (IR) absorption spectroscopy. The spectral analyses indicated that changes in Raman spectroscopy intensity occurring with increasing methane gas content were determined to be caused by changes in optically resonant components in the films. Furthermore, a significant correlation was seen between the relative intensity of IR peaks and wear durability.

Effect of microstructure and hydrogen content on the characteristics of amorphous hydrogenated carbon protective coatings

Amorphous hydrogenated carbon films have splendid wear characteristics as protective coatings. In the present work we have studied the relation between wear durability and microstructure of the amorphous hydrogenated carbon films prepared with radio‐frequency plasma‐enhanced chemical vapor deposition. Wear rates of pin‐on‐disk sliding tests for the films deposited at various conditions have been compared with the results of spectroscopic analysis. Wear durability of the films has been found to be described with a combination of two factors, one is the shoulder‐to‐main peak ratio of Raman spectra and the other is content of chemically bonded hydrogen atom. The former factor stands for the amount of ‘‘graphitelike’’ regions and the latter stands for the amount of ‘‘organic’’ regions in the carbon films.