Depth-Dependent Structural Changes in PS-b-P2VP Thin Films Induced by Annealing

GISAXS measurements with scattering contrast matching at the silicon K-edge were performed to obtain depth-resolved information on structural changes in as-spun and annealed PS-b-P2VP thin films on silicon substrate. Depth-sensitive GISAXS measurements of the as-spun film revealed a vertically oriented fingerprint-like lamellar structure with a microphase separation distance of 59 nm throughout the entire film. The annealed film showed a significantly reduced ordering at the surface to a depth of about 30 nm, while the order is preserved toward the substrate interface. At the same time, no significant transition to horizontal ordering was observed after 2 h of annealing at 105 degrees C. We conclude that the transition process from vertical to horizontal ordering is incomplete after the annealing time and remains in a frozen state at room temperature. Moreover, the transition starts as a disorder increase at the top of the film, which indicates a higher mobility of the coalescing microdomains at the surface.