Decay of interface correlation in thin polymer films

The long-range interface correlation in thin polymer films (polystyrene and fully brominated polystyrene) prepared by spin-coating is examined. Using diffuse X-ray scattering at small angles of incidence, the roughness correl ation which dominates the surface morphology of the polymer film is probed from mesoscopic down to molecular in-plane distances. At the smallest repli cable in-plane length scale, the crossover from a conformal to a statistica lly independent roughness spectrum is determined. The influences of molecul ar weight and film thickness are discussed. Compared to annealed samples, t he as-prepared ones show a different scaling behavior, which is explained w ith simple models taking surface-bending rigidity into account. With a real -time annealing investigation, the decay of interface correlation after the onset of annealing has been followed. At annealing even below the glass-tr ansition temperature, the roughness correlation is changing and disappears during sufficiently long annealing in the melt. Monitoring the changes with time probes the mobility of the polymer molecules at the polymer-vacuum in terface. In thin films, the time constant is increased. The determined surf ace diffusion coefficient shows a slowing down as compared to the bulk beha vior which may be attributed to the attractive, long-range substrate-interf ace interaction.