Depth-dependent structural analyses in PS-b-P2VP thin films as revealed by grazing incidence small angle scattering in the tender energy region

We report depth-resolved structural measurements in symmetric PS-b-P2VP thin films, using grazing incidence small angle X-ray scattering (GISAXS) in the tender X-ray region. The nanostructures in thin films show cylindrical structures although lamellar structures are expected, thermodynamically, as equilibrium state. It has been reported that, when the thin films are annealed at temperatures greater than the T_g, lamellar structures formed, parallel to the substrate. We prepared as-cast and annealed thin films on silicon substrates. From GISAXS measurements, we concluded that vertical cylindrical nanostructures in as-cast thin films are formed, oriented from surface toward substrate interface. Annealing changed the vertical cylindrical nanostructures at the surface. Even after very long annealing, like 12 hours above T_g, we found that vertical nanostructures still remained at the substrate interface, due to the lower mobility of polymer chains near the substrate interface.