The morphologies of poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) copolymer thin films were analyzed via atomic force microscopy and transition electron microscopy (TEM). The asymmetric copolymer thin films spin-cast from toluene onto mica presented meshlike structures, which were different from the spherical structures from TEM measurements. The annealing temperature affected the surface morphology of the PS-b-PDMS copolymer thin films; the polydimethylsiloxane (PDMS) phases at the surface were increased when the annealing temperature was higher than the PDMS glass-transition temperature. The morphologies of the PS-b-PDMS copolymer thin films were different from solvent to solvent; for thin films spin-cast from toluene, the polystyrene (PS) phase appeared as pits in the PDMS matrix, whereas the thin films spin-cast from cyclohexane solutions exhibited an islandlike structure and small, separated PS phases as protrusions over the macroscopically flat surface. The microphase structure of the PS-b-PDMS copolymer thin films was also strongly influenced by the different substrates; for an asymmetric block copolymer thin film, the PDMS and PS phases on a silicon substrate presented a lamellar structure parallel to the surface at intervals. (c) 2007 Wiley Periodicals, Inc.