Self-Alignment of Cylinder-Forming Silicon-Containing Block Copolymer Films

Well-ordered perpendicular cylinders of star-block copolymers (BCPs) composed of polystyrene and poly(dimethylsiloxane) blocks with high aspect ratio can be achieved by using a combination of architecture effect (entropy effect) and surface air plasma treatment (enthalpy effect). An interesting morphological evolution from disordered texture to hexagonally packed cylinders with perpendicular orientation has been observed, in which perpendicular cylinders are initiated at the top surface and bottom substrate of the thin film, followed by a self-alignment process, resulting in span-thru cylinders through the thin film. The self-alignment process is systematically examined by a combination of real space imaging using transmission electron microscopy, reciprocal space imaging using grazing incidence small-angle X-ray scattering, and three-dimensional tomography. The experimental results reveal a unique mechanism for the formation of highly ordered BCP thin films via surface-induced nucleation of perpendicularly oriented cylinders followed by lateral ordering of the cylinders. This discovery provides an insight into the mechanisms of confined self-assembly of BCP for the engineering of nanostructured thin films with controlled orientation and long-range order.