Raleigh L. Davis

Large-Area Nanosquare Arrays from Shear-Aligned Block Copolymer Thin Films

While block copolymer lithography has been broadly applied as a bottom-up patterning technique, only a few nanopattern symmetries, such as hexagonally packed dots or parallel stripes, can be produced by spontaneous self-assembly of simple diblock copolymers; even a simple square packing has heretofore required more intricate macromolecular architectures or nanoscale substrate prepatterning. In this study, we demonstrate that square, rectangular, and rhombic arrays can be created via shear-alignment of distinct layers of cylinder-forming block copolymers, coupled with cross-linking of the layers using ultraviolet light. Furthermore, these block copolymer arrays can in turn be used as templates to fabricate dense, substrate-supported arrays of nanostructures comprising a wide variety of elements: deep (>50 nm) nanowells, nanoposts, and thin metal nanodots (3 nm thick, 35 nm pitch) are all demonstrated.

Creating controlled thickness gradients in polymer thin films via flowcoating.

Flowcoating is a popular technique for generating thin (5-200 nm), substrate-supported polymer films. In this process, a reservoir of coating fluid is held between the horizontal substrate and a nearly horizontal blade above the substrate; a film of fluid is drawn out of the reservoir by moving the substrate. Accelerating the substrate produces a film with a thickness gradient, particularly useful for high-throughput measurements where film thickness is an important parameter. The present work compares experimental film thickness profiles with a model based on a Landau-Levich treatment to identify the experimental parameters which govern film thickness. The key parameters are the capillary number and the radius of curvature of the reservoirs static meniscus, which is set by the blade angle, gap height, solution reservoir volume, and contact angles of the fluid with the blade and substrate. The results show excellent quantitative agreement with the first-principles model; the model thus provides a design approach which allows a user to produce polymer thin films of virtually any desired thickness profile.

Mixed-morphology and mixed-orientation block copolymer bilayers

Block copolymers have attracted considerable attention due to their ability to self-assemble into highly regular structures, spanning length scales from several nanometers to over 100 nm. Block copolymers confined in thin films have been extensively utilized as soft templates for nanofabrication, but most applications have been restricted to single-layer templates with smectic and hexagonal symmetries. Here we show that a multi-step approach that includes shear alignment, thin film lift-off, and stacking can access novel three-dimensional block copolymer structures with long-range order and mixed symmetries. This technique allows control over the long-range order and also expands the range of nanolithographic templates accessible through guided self-assembly.