Morphology of ultrathin supported diblock copolymer films: Theory and experiment

An analysis of the morphological behavior of substrate-supported diblock co polymer films for thicknesses t below the equilibrium period L-0 of the cop olymer is presented. Substrate-supported films generally exhibit dissimilar interactions between the copolymer block components and the free and Subst rate surfaces. Accordingly, in this study, self-consistent-field calculatio ns that incorporate asymmetric surface energetics were used to assess equil ibrium film morphologies. Phase diagrams were constructed as a function of film thickness, surface interaction energies, the segmental interaction, an d the chain length. In conjunction, experiments were conducted on a series of polystyrene-b-poly(n-alkyl methacrylate) copolymer films supported by si licon substrates. These employed a novel atomic force microscopy technique that allowed for the precise tracking of morphology as a function of film t hickness. Comparison of the experimental results and calculations revealed several common trends. In particular, hybrid morphologies, incorporating bo th surface-parallel and surface-perpendicular elements, were observed both experimentally and through the calculations for the thickness regime, t sim ilar to 0.5L(0). The stability of such structures was found to be closely l inked to the symmetry of the surface energetics.