Directed Self-Assembly of Block Copolymers into Photonic Structures

Periodic structures can have many applications in optics, membrane design, and lithography. One method to achieve these are through the use of block copolymers with two chemically distinct moieties which are thermodynamically immiscible, which drives microscale phase separation and yields periodic structures. Mesoscale structures are typically limited in long-range periodic order due to uncontrolled nucleation and growth, but strategically placed defects can allow predetermination of nucleation sites and limit grain growth, affording control over the assembly process. Photonic response in polymeric materials is strengthened by well-defined long-range order and is key for the implementation of block copolymer-based photonic waveguides in visible-light integrated circuits. In this work, nanoscale pillars are fabricated in quasicrystalline or hexagonal patterns substrates using polymer-pen nanolithography (PPL) and electron beam lithography. PPL is a novel approach to precision assembly allowing high throughput of patterning soft materials onto a surface. The lithographic tools generate a durable and chemically selective surface-attached defect architecture to influence self-assembly of polydimethylsiloxane-b-polylactide block copolymer. The resultant structural characteristics of the pattern-assisted assembly are examined using X-ray scattering and microscopic capabilities. The influence of pre-patterned pillar structures on self-assembled structures of the block copolymers is discussed in terms of graphoepitaxy and free-energy landscape engineering.