Graduate Thesis Or Dissertation
 

Characterizations of silicon-germanium nanocomposites fabricated by the marine diatom Nitzschia frustulum

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  • Marine diatoms are a class of microalgae that possess cell walls composed of silica nanoparticles. These organisms actively assimilate silicic acid Si(OH)4 from seawater, polymerize silicic acid to silica nanoparticles by a protein-mediated precipitation process, and then assemble the silica nanoparticles into intricate patterns that constitute the cell wall microarchitecture (consists of around 30nm of SiO2 nanoparticles) of the diatom frustule. The biomineralization capacity of marine diatoms, Nitzschia,was harnessed to biologically manufacture silicon oxide / germanium oxide nanocomposite materials. Germanium was incorporated into living diatom cell mass by a two-stage cultivation process. The micro- and nanostructures of biogenic oxide nanocomposite before and after post processing were characterized by FT-IR, HR-TEM with EDX, and XRD. Photoluminescence (PL) measurements were performed on these biogenic nanocomposites after different post processing to remove the organics. Strong blue photoluminescence was observed from samples treated with H202 and oxygen plasma. However, no photoluminescence could be observed after NOT thermal annealing. A clear blueshift was observed from samples with the addition of germanium. Based on the comparison of the PL from diatom samples with that from synthesized silica, the self-trapped exciton (STE) affected by quantum confinement effect (QCE) is proposed as the mechanism of the PL from diatom.
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