Nanoscale surface topologies of non-neutral polymer adsorbed layers for the tailored control of BCP microdomain orientations

Nanoscale surface topography has received great attention for its ability to direct the self assembly of block copolymer (BCP) microdomain orientations in thin films. Here we report that the unique surface topological features of “non neutral polymer substrates” can be used to achieve highly aligned perpendicular lamellar orientation of BCP microdomains. The polymer substrates were composed of PS chains strongly adsorbed onto silicon substrates. Based on x-ray reflectivity and atomic force microscopy, we found that the thicknesses of the PS adsorbed layers remained constant (~2 nm in thickness) with different molecular weights (M_w), while the surface topologies changed from homogeneous for low PS to heterogeneous with a characteristic length of ~ 100 nm for high M_w PS. A lamellar forming PS-block-PMMA thin films were prepared on the polymer substrate. By using grazing incidence small angle X-ray scattering, we mapped out the phase diagram of BCP orientations at T =200 °C, a temperature which creates a neutral air surface so that the substrate surface is the only external field. The role of surface topologies in controlling the self assembly of BCP thin films from the buried interface will be discussed.