Januariyasa, I Komang (2024) Structuring Azobenzene-containing Materials in Three Dimensions with Light. [Tesi di dottorato]

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Abstract

The introduction of three-dimensional micro-architecture to the surface of the material has enabled the realization of a multitude of novel functionalities. The distinctive functionality is derived from the complex interplay between the three-dimensional architectural configuration and the surrounding environment, which separates it from the capabilities of planar or bulk versions of the materials. To date, photolithography has provided a robust methodology for the fabrication of microstructures with the aid of light. A multitude of photolithography techniques have been developed; however, they typically exhibit a trade-off between scalability for large-surface fabrication and flexibility for creating complex microstructures. Azopolymers, a type of polymer containing azobenzene molecules, have been proposed as a promising class of photo-responsive materials for the fabrication of structures on surfaces. The response of the azopolymer to light is strongly influenced by the intensity and polarization of the light, which offers a range of possibilities for creating microstructures on the surface. This Thesis presents novel ideas and concepts for utilizing the interaction between engineered light and the pre-structured azopolymer surface for the fabrication of three-dimensional micro-architectures. The first concept introduces the wavelength as a novel lithographic parameter for three-dimensionally controlling photodeformation of azopolymer-based micropillars. The application of different wavelengths results in varying degrees of deformation within the micropillar volume, ultimately leading to distinct microstructural morphologies. This approach allows for the straightforward generation of surfaces with distinct wettability characteristics through the use of two distinct wavelengths. The second concept is based on employing spatially engineered intensity of light to reshape azopolymer-based micropillars. The computer-generated holography technique was employed to generate any arbitrary spatial intensity pattern. By rationally designing the intensity patterns in relation to the geometric shape of the micropillar, a variety of geometric structures can be achieved. The third idea introduces an approach that employs a polarization rotator technique to generate spatially rotating polarization. The locally varying polarization provides a spatially reconfigurable driving force, enabling the free reshaping of azopolymer micropillars. This strategy allows for the creation of micro-architectures with tailored orientational features. Additionally, by modifying the scale of the beam in relation to the dimensions of the micropillar, it is possible to achieve different scales of orientational features. The concepts introduced here demonstrate the potential of azopolymer for fabricating complex three-dimensional micro-architecture on the surface, both in polarization-based and intensity-based control, drastically extending the range of potential applications.

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