Elastic modulus of polystyrene film from near surface to bulk measured by nanoindentation using atomic force microscopy

Using atomic force microscopy with a spherical indenter, we evaluated the surface and bulk elastic modulus of thick and thin polystyrene films. The elastic modulus of the thick films at penetration depths of more than 10nm was equivalent to that of bulk measured by a tensile test. In the thin films, the estimated values were greatly affected by the substrate material at penetration depths of more than 7nm. When the penetration depth was less than 5nm, however, the elastic modulus of both thin and thick films was slightly smaller than that of the bulk values.