Using a variable-energy direct carbon ion beam deposition technique, thin amorphous carbon films were grown on a silicon substrate. Interface modification was performed using C- energies in the range of 300–500 eV prior to the growth of the film to enhance adhesion of the film. By lowering the energy of the C- beam to 150 eV, amorphous carbon film was continuously grown after the interface modification. High-resolution electron microscopy illustrated that the silicon surface was severely damaged by 500 eV C- beam and the thickness of damage layer was about 15 nm. The carbon concentration profile in silicon as determined by electron energy loss spectroscopy showed that 500 eV C- beam implanted carbon into silicon up to 30 nm in depth and carbon was mixed with silicon in this implanted region. Silicon L-edge study at the C/Si mixed region found C–Si bonding formation only at the surface of silicon over 2–3-nm-thick layers. The damage layer or C/Si mixing was not observed at 300 eV C- beam modification. Wear testing found that strong adhesion occurred in samples modified at 500 eV, which indicated complete mixing at the interface. At 300 eV, modified samples exhibited delamination failure, which indicated inferior adhesion of the films. © 2000 American Vacuum Society.