Microstructure and mechanical properties of graphitic a-C:H:Si films

A series of graphitic a-C:H:Si films with different Si content were prepared by altering the sputtering current in a hybrid RF-PECVD and magnetron sputtering system. Microstructures and mechanical properties of them were characterized by IR, Raman, XPS, nanoindentation and scratch tests. Results show that although the sp3/sp2 ratio increases with increasing Si content and as high as 8.2 at.% of silicon was doped, the a-C:H:Si films remain graphitic in nature and the ID/IG ratio is nearly constant for all. The coupling effects of sputtering-induced heating and strong ion bombarding due to negatively biasing were considered to be responsible for the film graphitization. The graphitic nature also accounts for the lower nanohardness of prepared a-C:H:Si films than the diamond-like a-C:H and a-C:H:Si films.