A comparative study of the nanoscratching behavior of amorphous carbon films grown under various deposition conditions

Two types of amorphous carbon (a-C) films: one series with a layered struct ure (sequence of soft/hard carbon layers) resulting in thick, stable and sp (3) rich films, and another series of monolithic films rich in sp(2), were deposited on Si substrates by magnetron sputtering and were investigated wi th respect to their nanoscratching behavior. The main purposes of this work are to investigate the scratch performance of a-C films developed in layer ed structure and to compare this with the films rich in sp(2) content. Ultr alow load scratch tests were performed in the load range from 2 to 20 mN to explore the deformation mechanisms of such thin films and their adhesion t o the substrate. Below 5 mN, the scratches on layered structure films exhib it an almost full elastic response while on films rich in sp(2) content sho w massive brittle fragmentation. At 20 mN, the scratches on the former film s reveal some areas which are completely elastic and some areas which were typical of a buckle failure. These areas may correspond to hard and soft ca rbon layers, respectively. The coefficient of friction varied from similar to 0.2 to similar to 0.3, depending on the maximum normal load and being lo wer for films of the first type. Scratch testing results have shown that la yered structured films are resistant to plastic deformation during contact and, together with the stability of the thick layered films, support their potential for protective overcoats. (C) 2000 Elsevier Science S.A. All righ ts reserved.