Recent advances in atomic force microscopy (AFM) allow one to perform complex analysis of materials surfaces and near-surface regions with a nanometer scale resolution; this includes the imaging of surface topography and the measurements of stiffness, elasticity, hardness and nano-tribological characteristics. Understanding of the complex AFM response is still in its early stage, and it frequently requires the use of multiple complementary techniques. In the present work we have applied AFM for the study of the surface and nearsurface mechanical properties of plasma-treated polycarbonate. The results from AFM analysis, such as the stiffness and the relative Young modulus, were compared with the hardness values obtained by depth-sensing indentation and by the micro-scratch technique. The characteristics of the observed hardened surface layer are discussed with respect to the role of the “interphase” in adhesion en1hancement of plasma-deposited films on polymers.