Using atomic force microscopy and infrared spectroscopy, diamond-like carbon films deposited by r.f. plasma discharge were investigated. Hardness and roughness of the films strongly depend on the bias voltage of the substrates and thus the pressure in the deposition chamber. At higher pressures, the surface roughness of the films increases with their thickness. For films deposited at medium pressures, the roughness is almost constant regardless of the film thickness. At pressures below 53 Pa decreasing roughness is observed and hard films are obtained. These findings can be explained by the predominance of different species in the plasma. At low pressure, ionic species an accelerated towards sharp tips on the film surface leading to sputter removal of weakly bond material in these regions. At higher pressure neutral species in the plasma dominate. Thus, the balancing effect of sputtering is not observed. Hydrogen content and sp(3)/sp(2) ratios obtained from IR spectra revealed that the lower hardness of the rough surfaces can be explained by a higher content of sp(2) species in the films deposited at high pressure. Whereas the intensity ratio of sp(3)/sp(2) is almost constant for the films at higher pressure preferred sputter removal of sp(2) species leads to a significant increase of that ratio at low pressure.