Growth mechanisms of vapor-born polymer films

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The surface morphologies of poly(chloro-$p$-xylylene) films were measured using atomic force microscopy and analyzed within the framework of the dynamic scaling theory. The evolution of polymer films grown with fixed experimental parameters showed drastic changes in dynamic roughening behavior, which involve unusually high growth exponent $(\ensuremath{\beta}=0.65\ifmmode\pm\else\textpm\fi{}0.03)$ in the initial growth regime, followed by a regime characterized by $\ensuremath{\beta}\ensuremath{\sim}0$, and finally a crossover to $\ensuremath{\beta}=0.18\ifmmode\pm\else\textpm\fi{}0.02$ in a steady growth regime. Detailed scaling analysis of the surface fluctuation in Fourier space in terms of power spectral density revealed a gradual crossover in the global roughness exponent, analogous to a phase transition between two equilibrium states, from a morphology defined by $\ensuremath{\alpha}=1.36\ifmmode\pm\else\textpm\fi{}0.13$ to the other morphology characterized by $\ensuremath{\alpha}=0.93\ifmmode\pm\else\textpm\fi{}0.04$ as the film thickness increases. Our experimental results which significantly deviate from the well established descriptions of film growth clearly exhibit that the dynamic roughening of polymer film is deeply affected by strong molecular interactions and relaxations of polymer chains.