Dynamic Thermal Field-Induced Gradient Soft-Shear for Highly Oriented Block Copolymer Thin Films

As demand for smaller, more powerful, and energy- efficient devices continues, conventional patterning technologies are pushing up against fundamental limits. Block copolymers (BCPs) are considered prime candidates for a potential solution via directed self-assembly of nanostructures. We Introduce here a facile directed self-assembly method to rapidly fabricate unidirectionally aligned BCP nanopattems at large scale, on rigid or flexible template-free substrates via a thermally induced dynamic gradient soft-shear field. A localized differential thermal expansion at the interface between a BCP film and a confining polydimethylsiloxane (PDMS) layer due to a dynamic thermal field imposes the gradient soft-shear field. PDMS undergoes directional expansion (along the annealing direction) in the heating zone and contracts back in the cooling zone, thus setting up a single cycle of oscillatory shear (maximum lateral shear stress similar to 12 x 10(4) Pa) in the system. We successfully apply this process to create unidirectional alignment of BCP thin films over a wide range of thicknesses (nm to mu m) and processing speeds (mu m/s to mm/s) using both a flat and patterned PDMS layer. Grazing incidence small-angle X-ray-scattering measurements show absolutely no sign of isotropic population and reveal >= 99% aligned orientational order with an angular spread Delta theta(twhm) <= 5 degrees (full width at half-maximum). This method may pave the way to practical industrial use of hierarchically patterned BCP nanostructures.