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| Home > Documents in process > Metrology Of Sub-10 nm Block Copolymers To Control The Crystallization And Microphase Separation |
| Dissertation / PhD Thesis | PUBDB-2025-04061 |
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2025
Hamburg
Please use a persistent id in citations: urn:nbn:de:gbv:18-ediss-131082
Abstract: Properties of polymers are largely governed by their structure on the nanoscale. Therefore, precise control over polymer morphology enables novel design strategies for bottom-up nanofabrication and the tailored fabrication of emerging functional nanomaterials. However, the vast structural and chemical diversity of polymers requires extensive case-by-case investigation, resulting in a sustained effort to elucidate the relationship between morphology and properties. Especially in thin films, the nanoscale modulation of the topography leads to pronounced interfacial effects, with direct implications for the development of structured, functional nanomaterials.This cumulative thesis studies dynamic processes in polymer thin films with in situ Atomic Force Microscopy (AFM), aiming to provide specific suggestions and developing novel strategies for the design of nanomaterials.First, a conductive, perchlorate-doped polypyrrole (PPY) thin film is investigated using in situ electrochemical Atomic Force Microscopy (EC-AFM). In electrolyte, the film thickness, roughness, and elastic properties closely follow the applied electric potential, revealing a correlation between film topography and elastic properties. Repeated potential cycling results in osmotic expansion of the film and passive swelling. Furthermore, the rough nodular PPY topography leads to a highly heterogeneous distribution of the elastic modulus on the film surface. These findings have important implications for the future design of conductive polymer interfaces in electroactive devices, potentially improving overall device lifetime and performance.The design of interfaces is particularly relevant in the field of block copolymer (BCP) thin films, since interfacial energies govern the orientation of microphase-separated BCP domains. Bottom-up self-assembly techniques have emerged as a promising tool for the fabrication of patterned surface nanostructures. However, for next-generation lithography, nanofabrication has to advance towards the sub-10 nm regime, requiring the development of highly segregating, short-chain BCPs, so-called ’high χ, low N’ BCPs.In the second study, thin films of a double-crystalline, short-chain poly(ethylene)-block-poly(ethylene oxide) (PE-b-PEO) are investigated on neutral substrates using in situ AFM with a heating stage. It is demonstrated how the BCP films form defined, extended-chain vertical lamellae during thermal annealing. The lamellae formation mechanism is identified as breakout crystallization, which disrupts the initially microphase separated morphology. This is attributed to the surface energy changes associated with crystallization of extended-chain crystals. Additionally, the results demonstrate that macroscopic alignment of the nanolamellae is achievable with physical guiding patterns, providing a novel pathway for bottom-up nanofabrication towards the sub-10 nm regime. These findings illustrate how the effective segregation strength can be improved by crystallization and that extended-chain crystallization offers a unique way of direct control over the pitch of the lamellar nanostructures.Furthermore, the PE-b-PEO thin films are exposed to solvent vapor atmosphere to investigate the influence of solvent exposure on the annealing dynamics and morphology. By varying the solvent vapor annealing (SVA) conditions, standing cylinder morphologies or vertical lamellae can be observed. It is found that the final SVA morphologies are significantly affected by the initial chain orientation in the film due to slow kinetics at the chosen annealing temperature. Although the solvent promotes chain mobility in the BCP to some degree, the low annealing temperature restricts structural reorganization during SVA. These results emphasize the needto extensively study the chain kinetics during SVA in order to elucidate potential kinetic pathways for the formation of surface nanostructures.In conclusion, the present work illustrates that the interfaces of polymers play a pivotal role in influencing the morphology and properties of polymer thin films. Correlating internal structure and surface effects is essential for further advancing polymer-based nanotechnology and developing novel functional nanomaterials. Furthermore, dynamic in situ studies of these processes are crucial for understanding the structure-property relationship in polymer thin films. Therefore, this work contributes to the efforts in the development of novel bottom-up nanofabrication techniques by providing valuable insights to the structure-property relationship of polymers.
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