The surfaces of thermally annealed thin polystyrene films on silicon were i
nvestigated by specular and diffuse x-ray scattering. The data cannot be in
terpreted satisfactorily with capillary wave calculations assuming attracti
ve van der Weals substrate film interactions. The analysis shows that polys
tyrene films coated on silicon substrates are in a strongly confined state
even for film thicknesses much larger than the radius of gyration, possibly
due to strong confinement that arises from the interaction. at the polymer
/substrate interface and the viscoelastic behavior of the thin films.