Photopatterning of cross-linkable epoxide-functionalized block copolymers and dual-tone nanostructure development for fabrication across the nano- and microscales

Autonomous discovery of emergent morphologies in directed self-assembly of block copolymer blends

The directed self-assembly (DSA) of block copolymers (BCPs) is a powerful approach to fabricate complex nanostructure arrays, but finding morphologies that emerge with changes in polymer architecture, composition, or assembly constraints remains daunting because of the increased dimensionality of the DSA design space. Here, we demonstrate machine-guided discovery of emergent morphologies from a cylinder/lamellae BCP blend directed by a chemical grating template, conducted without direct human intervention on a synchrotron x-ray scattering beamline. This approach maps the morphology-template phase space in a fraction of the time required by manual characterization and highlights regions deserving more detailed investigation. These studies reveal localized, template-directed partitioning of coexisting lamella- and cylinder-like subdomains at the template period length scale, manifesting as previously unknown morphologies such as aligned alternating subdomains, bilayers, or a "ladder" morphology. This work underscores the pivotal role that autonomous characterization can play in advancing the paradigm of DSA.

Spatial arrangement of block copolymer nanopatterns using a photoactive homopolymer substrate

Spatial control of the orientation of block copolymers (BCPs) in thin films offers enormous opportunities for practical nanolithography applications. In this study, we demonstrate the use of a substrate comprised of poly(4-acetoxystyrene) to spatially control interfacial interactions and block copolymer orientation over different length scales. Upon UV irradiation poly(4-acetoxystyrene) undergoes a photo-Fries rearrangement yielding phenolic groups available for further functionalization. The wetting behaviour of PS-b-PMMA deposited on the poly(4-acetoxystyrene) films could be precisely controlled through controlling the UV irradiation dose. After exposure, and a mild post-exposure treatment, the substrate switches from asymmetric, to neutral and then to symmetric wetting. Upon exposure through photomasks, a range of high fidelity micro-patterns consisting of perpendicularly oriented lamellar microdomains were generated. Furthermore, the resolution of chemically patterned poly(4-acetoxystyrene) substrate could be further narrowed to submicrometer scale using electron beam lithography. When the BCP was annealed on an e-beam modified poly(4-acetoxystyrene) surface, the interface between domains of parallel and perpendicular orientation of the BCPs was well defined, especially when compared with the substrates patterned using the photomask.

Simultaneous In-Film Polymer Synthesis and Self-Assembly for Hierarchical Nanopatterns

A key requirement for practical applications of nanostructured block copolymer (BCP) self-assembly is the ability to generate complex geometries including different shapes and diverse sizes across one substrate surface. This has been difficult because spatial control over the underlying chemistry of the BCP has been limited. Here, we demonstrate a photocontrolled in-film polymerization process in the presence of monomer vapor for synthesizing homopolymers in self-assembled BCP films. The homopolymers blend with BCPs and alter the nanopatterns by changing the underlying polymer chemistry and composition. We apply this technique to a variety of BCPs including polystyrene-b-polyisoprene-b-polystyrene, polystyrene-b-poly(methyl methacrylate), and polystyrene-b-poly(4-vinylpyridine). The region of in-film polymerization can be modulated by the location of irradiation using photomasks for obtaining distinct morphologies on one substrate, providing a new platform for hierarchically manipulating nanopatterns within the self-assembled BCP thin film as well as opening up a new area for radical polymerizations of monomers within such geometrically confined, swollen films.

UV-solvent annealing of PDMS-majority and PS-majority PS-b-PDMS block copolymer films

The response of polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) thin films to UV exposure during solvent vapor annealing is described, in order to improve their applicability in nanolithography and nanofabrication. Two BCPs were examined, one with the PS block as majority (f _PS = 68%, M _n = 53 kg mol^-1), the other with PDMS block as majority (f _PDMS = 67%, M _n = 44 kg mol^-1). A 5 min UV irradiation was applied during solvent vapor annealing which led to both partial crosslinking of the polymer and a small increase in the temperature of the annealing chamber. This approach was effective for improving the correlation length of the self-assembled microdomain arrays and in limiting subsequent flow of the PDMS in the PDMS-majority BCP to preserve the post-anneal morphology. Ordering and orientation of microdomains were controlled by directed self-assembly of the BCPs in trench substrates. Highly-ordered perpendicular nanochannel arrays were obtained in the PDMS-majority BCP.

Photopatterning of Block Copolymer Thin Films

Block copolymers are potentially useful materials for large-area 2-D patterning applications due to their spontaneous self-assembly into sub-50 nm domains. However, most thin film engineering applications require patterns of prescribed size, shape, and organization. Photopatterning is a logical choice for manipulating block copolymer features since advanced lithography tools can pattern areas as small as a single block copolymer domain. By exposing either the block copolymer or a responsive interfacial surface to patterned radiation, precise control over placement, orientation, alignment, and selective development of block copolymer domains can be achieved. This Viewpoint highlights some of the recent research in photopatterning block copolymer thin films and identifies areas of future opportunity.