Morphologies of Surface Perforations and Parallel Cylinders Coexisting in Terraced Films of Block Copolymer/Homopolymer Blends with Oxygen Plasma Etching.

This study has demonstrated how oxygen plasma etching carves surface structures for thin films of polystyrene-block-poly(methyl methacrylate)/homopolystyrene blends. By tuning the weight-fraction ratio, blend films form perforations and cylinders on the SiOx/Si substrate. Since perforations exist only on the free surface and substrate interface, short exposure to oxygen plasma to quickly etch the PMMA component produces distorted hexagonal arrays of nanodots on the free surface. The interior of the blend films forms polygrain micro-structures composed of parallel cylinders with an in-plane random orientation. Oxygen plasma etching imposed on the fractured surfaces results in five morphologies: (i) distorted hexagonal arrays of nanoholes, (ii) layer-by-layer stacks, (iii) zigzag-like arrays, (iv) intertwined rectangular arrays of nanodots and nanoholes, and (v) intertwined parallelogram arrays of nanodots and nanoholes. The morphologies suggest synergic effects of grain orientations, stresses, spatial confinement, local segregation of chains, and etching kinetics on the terraced films with oxygen plasma etching.