Defect Patterning for the Directed Self-Assembly of Block Copolymers using Polymer Pen Nanolithography

Block copolymers (BCPs) with two or more immiscible and covalently linked blocks will have the propensity to phase separate at the nanoscale. Given sufficient processing, these phase-separated domains conform to periodic structures that have been useful in lithography, optics, and membrane design. Typically, resulting structures are limited in long range order due to uncontrolled nucleation kinetics. A strategy for placing defects on a substrate can assist in the assembly of ordered structures by pre-determining nucleation sites and regulating grain growth. Improved long-range order strengthens photonic response in BCPs and is a key factor in successfully incorporating them into visible-light integrated circuits as waveguides. Here, a substrate is pre-patterned with a poly(dimethylsiloxane) (PDMS) photoresist using polymer-pen nanolithography (PPL). The PPL technique is a novel approach to precise and high throughput application of soft material features onto a surface. The PDMS resist is photopolymerized to yield a chemically selective defect architecture intended to influence the self-assembly of a PDMS-b-poly(ethylene-alt-propylene) BCP previously found to assemble into periodic structures. The structural characteristics of the patten-assisted assembly is analyzed using microscopy and X-ray scattering techniques.