Structure and tribological behavior of amorphous carbon films implanted with Cr₊ ions

Amorphous carbon (a-C) films were deposited on a single-crystal silicon substrate by direct current magnetron sputtering system. The effect of Cr⁺ ion-implantation on the structure and tribological properties of the sputtered a-C films were investigated by means of Raman spectrometric analysis, X-ray photoelectron spectroscopic analysis, and friction and wear measurements. The morphology of the worn film surfaces was observed with a scanning electron microscope (SEM). The structure of a-C tended to be disordered and had a growth of sp³ content at high implantation doses. The sputtering depth profiles of the films by X-ray photoelectron spectroscopy indicate that chromium carbide is formed at the film-substrate interface where the implanted Cr⁺ has a higher concentration. The interface between Si and C is widened by ion-implantation. Thus the anti-wear behavior of the ion-implanted film is improved. The brittleness of the a-C film is increased after implantation with Cr⁺ at a larger dose. This is attributed to the generation of chromium carbide from the reaction of carbon and Cr. Subsequently the film implanted with Cr⁺ at a relatively low dose is characterized by adhesive wear, while that implanted at a higher dose characterized by abrasive wear.