| Abstract: | The morphologies of thin, substrate-free block copolymer films have been examined by cross-sectional TEM. Two poly(styrene-b-butadiene) diblock copolymers were studied: one that forms PS cylinders and the other that forms PB cylinders in the bulk. Films were annealed while supported by metal TEM grids, embedded, and ultramicrotomed in crosssection. We find that at the metal support the film forms a meniscus-like region, or Plateau border, which exhibits the bulk morphology. Away from the border, the film thickness decreases and regions of terraced in-plane cylinder domains occur until a minimum thickness is reached. The minimum thickness region of the PB majority copolymer in cross-section shows a PS interlayer penetrated by a hexagonal array of circular PB channels that connect upper and lower PB surface layers, and a total thickness of 25–27 nm. The minimum thickness region of the PS majority copolymer in plan view shows no image contrast, but in cross-section reveals a continuous PS interlayer covered by layers of PB, and a total thickness of 20 nm. Comparisons with the chain dimensions suggest a bilayer arrangement for both morphologies with strongly perturbed chain conformations in the surface layers. © 1996 John Wiley & Sons, Inc. |
