(415a) Manipulating Ordering and Orientation in Nanostructured Thin Films By Combining Substrate and Solvent Annealing Effects

Block polymer (BP) thin films potentially can be used to template large arrays of nanopatterns for advanced nanotechnologies.  However, the practical utilization of directed BP self-assembly typically requires guide patterns of relatively small size scales.  Two areas of recent progress in our research group include (1) the detailed tuning of substrate surface energetics to probe the ordering and orientation of BP thin films, and (2) the use of solvent vapor annealing to manipulate nanoscale morphologies and achieve well-oriented nanostructures.  In the first case, we are systematically examining the influence of the substrate surface energy on wetting behavior, through-film interactions, and substrate surface field propagation. Notably, we have determined the applicability of decoupled surface energy components (dispersive and polar interactions) vs. total surface energy formalisms.  Our experimental results combined with surface chemistry literature indicate repulsive total surface energy interactions are the dominant force at the substrate-polymer interface, whereas attractive decoupled surface energy interactions become significant past the contacting layer.  This effort provides a blueprint for the generalized design of substrate surfaces that achieve target BP nanostructure orientations.  In the second case, we are exploring the macroscopic alignment of BP nanostructures on a template-free substrate through raster solvent vapor annealing combined with soft shear (RSVA-SS).  Our spatial control over nanoscale structures allows one to uniquely ‘write’ macroscopic patterns with microscopically aligned BP nano-features.  This method significantly improves on previous approaches by eliminating the correlation between the BP alignment and shearing-pad shape, allowing continuous fabrication of highly ordered BP patterns in a two-dimensional manner.  We demonstrate that complex patterns such as dashes, crossed lines, and curves can be imparted easily to thin films on featureless and untreated substrates. Furthermore, the ability to expand or shrink the “writing” size of the oriented regions from millimeters to centimeters provides a unique handle for manipulating pattern formation in an on-demand fashion.