Academic Awards 2023 booklet

77 Exploring the Morphology, Chemistry, and Mechanics of Biogenic Silica in Diatoms Through the evolutionary process for millions of years, many living organisms have discovered a way of creating hierarchical biogenic materials. The development of characterization techniques that lead to discovering various properties of such materials can provide unique opportunities not only to advance our understanding of the properties and behavior of these materials but also to utilize the obtained knowledge in the fabrication of man-made materials with improved proper-ties. These biogenic materials can even be produced from basic ingredients such as silica (“sand”) which is found in the diatom “glass house” exoskeleton. In this research, we aimed to understand how diatoms form their silica exoskeleton structure, and what changes happen in their properties while Al ions are present or salt levels vary in the growth medium. To this end, we designed a new toolbox to precisely cut and isolate different parts of the diatom exoskeleton inside Scanning Electron Microscope. Then, the mechanical properties of the cut parts of the diatom exoskeletons were individually determined at microme-ter length scale. It was discovered that not only different parts of the diatom exoskeleton can have different mechanical properties, but also they behave differently upon the presence of Al ions in the growth medium or changes in the amount of fed salt. Furthermore, various challenges related to sample preparation and handling, in situ observation of specimen behavior upon de-formation, and conducting real-time mechanical testing on micro-scale specimens were addressed in our approach. The findings and the developed toolbox in this thesis may pave the way for materials scientists to characterize and improve the properties of glass-based coatings for indus-trial applications. Figure 1: SEM image of exterior surface of an isolated valve of diatom Thalassiosira pseudonana. Figure 3: Schematic illustration of the in situ fabrication, manipulation, and mechanical testing work-flow of free standing silica beams inside SEM. Figure 2: Scheme of in situ isolation, transfer, and deformation of constituents of a diatom exoskeleton inside SEM.