Fabrication and applications of metallic and polymeric smart materials using two-photon lithography
Lee, Mian Rong
Date of Issue2018-01-02
School of Physical and Mathematical Sciences
This thesis details my PhD research from the past four years focused on the fabrication and applications of metallic and polymeric shape-shifting “smart” materials using the technique of twophoton lithography. I begin the thesis with a brief introduction into the principles of two-photon lithography, followed by applications of two-photon lithography in the fabrication of polymeric shapeshifting materials, and the direct laser writing of metallic structures. From the fabrication of polymeric shape-shifting materials, the main challenges I identify are that currently, (1) most of the polymeric shape-shifting materials are macroscale, and (2) usually exhibit only directional shape change such as bending or twisting. I aim to resolve these issues by demonstrating the fabrication of 10 - 30 μm sized shape-shifting protein microstructures that are not only able to undergo quantifiable directional shape-shifting (chapter 2), but also geometrical shapeshifting from circles to polygons such as triangles, square, pentagons and hexagons (chapter 3). I also discuss some of the challenges faced in direct metal writing; for instance, although direct metal writing has been explored extensively for the past decade, most fabricated structures comprise sparse, or dense but irregularly shaped nanoparticles. I aim to fabricate monodisperse, dense gold nanoparticle microstructures where the physical and optical properties can be tuned by varying surfactant concentration, and fabricate these microstructures within a microfluidic channel for SERS sensing of small gaseous molecules (chapter 4). I also recognise that the precision and morphology of fabricated metallic structures are largely dependent on the fabrication parameters and composition of the photoresist used, however, an investigation into the effects of varying fabrication parameters on the resulting structure is lacking. Hence, I create a robust Au precursor solution and optimized the writing parameters to fabricate highly precise, well-defined Au microstructures even after long hours of lithography (~4 hours) (chapter 5). Finally, I conclude the thesis with a short summary and outlook to discuss future work in the field of two-photon fabrication (chapter 6).