Study on Internal Structure Characterization of Nanoholes and Densely Branched Morphology Thin Films

The internal structures of thin films, having nanoholes and densely branched morphologies and prepared from a long chain polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymer, were characterized. Using grazing-incidence small- and wide-angle X-ray scattering (GISAXS & GIWAXS), the thickness of the lamellar mesophase repeat unit and the orientation of the PEO crystalline chain stems within the thin film were determined. The dimensions of the internal structures and their orientations were linked to the surface morphologies measured by atomic force microscopy. For the nanoholes morphology, the film thicknesses were found to deviate from an integer multiple of the diblock copolymer lamellar units (~ 70 nm) promoting the hole textures. Dewetted architectures were obtained by annealing freshly prepared films under toluene/water vapour environment at an elevated temperature. After that, some PEO chains were able to crystallize within the dewetted large holes resulting in a densely branched morphology (DBM). The crystalline chain stems of the crystalline lamellar, within the dewetted large holes, were found to be roughly perpendicular to the film substrate with thicknesses of about 10 nm. This is in agreement with the diffusion-limited aggregated model.