In this paper, a dynamical force microscopy study of self-assembled monolayers of organosilanes, grafted onto a silica support, is reported. Organosilanes, terminated either with a functional group (ethylene glycol) or with a methyl group, were used. The influence of the reaction time and the solvent composition on the grafting was investigated to improve the homogeneity of the self-assembled monolayers. Numerical simulations of approach-retract curves, obtained in the tapping mode, were performed and compared to experimental ones. Information such as mechanical response and height of the grafted organic layers has been obtained.