Atomic force microscopy (AFM) has been used for nanotribological studies of silicon surfaces covered by oxide layers of various kinds: chemical oxides prepared by SC 1 (NH₄OH/H₂O₂/H₂O) and SC 2 (HCl/H₂O₂/H₂O) treatments, a thermally treated silicon surface and a H-terminated oxide-free silicon surface. Only in the case of SC 1 chemical oxide, scratching of the oxide and ploughing of the silicon by a Si₃N₄ AFM tip were observed. On the other hand, no wear of the sample was noted on other surfaces. By annealing the SC 1-treated surface in N₂ gas above 200^oC for 30 min, the oxide layer could not be scratched. By soaking the thermal oxide in KOH, the oxide layer was then scratched. It is suggested that the presence of OH bases is a requirement for the nano-scratching of the oxide layers.