Investigation of the structure and tribological properties of laser-irradiated hydrogenated amorphous carbon films

The pulsed laser to irradiate the surface of a hydrogenated amorphous carbon (a-C:H) film surface and subse-quently evaluated the resultant changes in the carbon bonding distribution in the irradiated area and the change in the surface topography. And, the tribological properties of the laser-irradiated films were evaluated. The laser irradiation of the a-C:H film surface increased the sp2 carbon bonding by the short duration of heating and pressurization due to the laser-irradiation. The surface shape changed from flat to convex by the irradiations, and its cross section was hemispherical. The hemispherical shape was attributed to the effect of cavities creation inside the film by laser-irradiation. Ball on disk sliding tests showed that the friction coefficient of laser -irradiated films was lower than that of the non-irradiated films. This is due to increase in the sp2/(sp2+ sp3) carbon ratio and to a decrease in the contact area with the ball as a result of the surface topography. After these sliding tests, the film topography of the laser-irradiated a-C:H films after sliding were changed to a flat surface because of the breaking of cavities during initial sliding. However, the friction coefficient did not become greater than that of non-irradiated a-C:H films. The reduction of the friction coefficient by laser irradiation of a-C:H films is related to the formation of transfer layer at initial sliding. These results indicated that the laser irradiation of a- C:H films is an effective surface treatment to improve their performance as a solid lubricating layer by changing the sp2 carbon bonding.