| dc.description.abstract | The present work focuses on the effects of film instability on micro-scale structure, surface roughness and ordering of cylindrical nanodomain in P(S-b-MMA) ultrathin block copolymer film on bare silicon substrates (SiOx/Si) and substrates coated with end-grafting PMMA (PMMA-SiOx/Si) and PS (PS-SiOx/Si) homopolymers. If the initial film thickness of thin films was incommensurated with an intracylindrical spacing, thermal annealing lead to relief structures with smooth free surface so as to achieve the commensurability of film thickness with the intracylindrical spacing. The diffuse scattering streaks were observed at angles with respect to film normal direaction in GISAXS patterns, and the diffuse streaks were found to correlated with the formation of relief structures. The relief structures have a facet-like wedge at the edge, resulting from partial wetting of the non-anchored P(S-b-MMA) top layer at contact angle in the range 4-6.5o on a autophobic P(S-b-MMA) wetting layer anchored onto the polar substrate. As a result, the dewetted morphologies via a mechanism of nucleation and growth strongly influences the spatial and ordering behavior of the nanodomains. At early stages of film instability, the formation of parallel-oriented PMMA cylindrical nanodomains increases the deformation energy and it further persists to force the shape of relief structures between irregular holes to have a facet-wedge shape. However, those relief structures are expected to be not at equilibrium. At high temperatures, the relief structures between irregular holes progressively developed to form drops accompanied by a transformation of cylindrical into noncylindrical nanodomains at curved surfaces. In contrast, for symmetric wetting boundaries on PS-SiOx/Si, thin film that resisted dewetting on a PS brush have a rough free surface due to the film commensurability. In the absence of undulations in thickness, a perturbation, as result of chain stretching, in the inter-domain spacing yielded small in-plane randomly oriented monograins on PS-SiOx/Si. Consequently, the free surface roughening was allowable to occur due to preferential segregation of excluded polymer chains from monograin boundaries onto the free surface.
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