Keywords: a-C; amorphous carbon; a-C: H; hydrogenated amorphous carbon (a-C:H); UHWMPE; ultra-high-molecular-weight polyethylene; a-C:H:Cr; chromium doped hydrogenated amorphous carbon (a-C:H); a-C:H:Ti; titanium doped hydrogenated amorphous carbon (a-C:H); a-C:N;