We　report　on　the　structural　evolution　and　low-friction　behaviour　of　silicon　(Si)　doped　amorphous　carbon　(a-C)　films.　Si-doped　a-C　films　were　fabricated　by　controlling　the　magnetron　Si　target　currents　under　an　electron　cyclotron　resonance　(ECR)　plasma　system.　Structural　analysis　indicated　that　Si　atoms　doped　into　the　a-C　lattice　preferentially　replaced　certain　sp3　C　atoms,　and　subsequently　formed　bonds　with　other　sp3　C　atoms.　Nanoindentation　and　nanoscratch　tests　showed　that　the　Si-doped　a-C　films　had　hard　surfaces　with　a　hardness　of　approximately　24　GPa　and　a　scratch　depth　of　40–60　nm.　Ball-on-disk　tribological　evaluations　further　showed　that　these　films　exhibited　low-friction　behaviour,　with　a　minimal　friction　coefficient　of　0.02.　Detailed　transfer　film　characterisation　revealed　the　formation　of　rich　oxide　and　graphene　structures　within　the　stable　contact-sliding　interface　of　the　Si-doped　a-C　film.　The　low　friction　mechanism　was　summarized　as　H–H　interactions　from　the　surface　terminal　passivation　of　Si　dangling　bond　with　hydroxide　(-OH)　or　hydrogen　(-H)　groups　and　π*-π*　interactions　occurring　between　the　graphene　layers　co-reducing　the　friction　force.　These　findings　shed　light　on　the　significance　of　doped　Si　atoms　in　the　structural　design　and　low-friction　applications　of　carbon　films.　©　2023