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Abstract
The spontaneous self-assembly of block copolymers (BCPs) into a variety of morphologies makes these systems desirable templates for lithography-based applications, including next generation energy storage and filtration membranes. BCP thin films are sensitive to their preparation and operational environments, which often involve solvents or high temperatures and are limited in the extent of control over local thickness variations. As such, understanding the dynamic properties and organization of polymer thin films in these environments is critical for achieving control over the nanopattern structures, a goal for fundamental science as well as technology applications. Atomic force microscopy (AFM) offers a unique characterization method to capture the real-time dynamics of these systems non-destructively and with application-relevant conditions, including imaging at high temperatures. The research presented in this thesis utilizes environmentally controlled AFM to directly observe the dynamics of terrace and hole formation in incommensurate BCP thin films, as well as domain interfacial fluctuations in confinement with lithographic templating using environmentally controlled AFM at high temperatures. These studies contribute to the understanding of the influences of structural defects and thermal fluctuations on nanopatterns, and how this disorder defines the limits of perfection in these films. BCP thin films are sensitive to local thickness variations and will form terraces and holes if the thickness is incommensurate. AFM imaging at high temperatures allows capture of the complete spatiotemporal evolution of the terraces and holes, revealing details of the thickness-dependent nucleation, growth, and coarsening mechanisms. Many applications for templated block copolymer films require long-range order that extends over wafer size scales and a variety of methods, known as directed self-assembly (DSA), have been employed to control the domain ordering in these films. Despite the perfect linearly achieved with DSA techniques, disorder persists in the form of thermal fluctuations and pattern roughness. Slow-scan-disabled AFM increases the effective imaging time resolution such that these interfacial fluctuations can be captured in real time. Additionally, imaging at high temperatures captures the dynamics and interfacial fluctuations around individual defects in topographically confined cylinder-forming PS-b-PMMA, revealing the pathways by which defects evolve and annihilate during thermal annealing and how these structural defects influence thermal fluctuations of the polymer film.
Finally, environmental AFM is extended to characterize the local transport of redox mediators through membranes in liquid environments with combined scanning electrochemistry-atomic force microscopy (SECM-AFM). Understanding transport at the single-pore level is a crucial component towards the development of novel materials to meet increasing demands on water filtration. Overall, this thesis seeks to understand the influences of confinement on ordered block copolymer systems with advanced AFM techniques.