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Synthesis and Characterisation of Barium Titanate Nanoparticles for Second Harmonic Generation Applications.

Matar, Omar (2017) Synthesis and Characterisation of Barium Titanate Nanoparticles for Second Harmonic Generation Applications. Integrated PhD and Master thesis, University of Leeds.

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This thesis presents findings of hydrothermally synthesised barium titanate nanoparticles for biomarker applications. Hydrothermal barium titanate (H-BT) and barium strontium titanate (H-BST) nanoparticles were successfully synthesised and were characterised for their second harmonic generation applications. X-Ray powder diffraction (laboratory and synchrotron) highlighted that H-BT and H-BST had a mixed tetragonal and cubic phase fraction present by Rietveld peak fitting analysis. Regardless of the phase fractions present, all nanoparticles emitted SHG (including a commercial cubic BaTiO3 sample that appeared cubic by XRD). The smaller sized H-BST nanoparticles (45 nm) required an increase in incident laser power compared to the H-BT sample (~140 nm). The phase of the nanoparticles and origin of SHG was investigated by electron diffraction, electron energy loss spectroscopy and high resolution HAADF-STEM imaging. In-situ electron diffraction of barium titanate showed that the tetragonal diffraction pattern transformed to a cubic pattern when heated above the Curie point. The phase transition was also investigated by EELS measurements of the Ti-L3 edge t2g-eg peak separation at room temperature and 400 oC showing the reduction in t2g-eg peak separation when the sample transforms from a tetragonal to cubic phase. The surface of the nanoparticles also showed an atomically rough layer with incomplete unit cells, and the ‘bulk’ of the nanoparticles showed random Ti-atom distortions by HAADF-STEM Ti-atom displacement analysis. This suggests the origin of SHG is likely to be both a cause of surface roughness and local asymmetric distortions in the nanoparticle bulk. The hydrothermally prepared and PLL-coated nanoparticles were measured to assess the cell viability and DNA damage of cells after a 24-hour exposure. The nanoparticles were measured by dynamic light scattering to understand the behaviour of uncoated and PLL-coated nanoparticles suspended in different media. The uncoated nanoparticles showed little reduction in cell viability and genotoxicity, whereas the PLL coated nanoparticles showed a reduction in cell viability and a failed comet assay at concentrations ≥10 µg/mL. The nanoparticles were confirmed to be taken up into the cells by electron microscopy of critically point dried and resin embedded cell sections. Cryo-TEM of the H-BT-PLL nanoparticles suspended at 100 µg/mL in complete cell culture media showed that some nanoparticles were coated with a calcium phosphate coating and others not. This resulted in, either cells having a direct exposure to PLL and positively charged nanoparticles, or all the calcium was removed from the media that is required for cell signalling pathways which could lead to a reduction in cell viability.

Item Type: Thesis (Integrated PhD and Master)
Related URLs:
Keywords: Barium Titanate, Nanoparticles, BaTiO3, EELS, resin-embedded cell section imaging, Cryo-TEM of nanoparticles in cell media.
Academic Units: The University of Leeds > Faculty of Engineering (Leeds) > School of Chemical and Process Engineering (Leeds)
Identification Number/EthosID: uk.bl.ethos.724388
Depositing User: Mr Omar Matar
Date Deposited: 09 Oct 2017 10:45
Last Modified: 25 Jul 2018 09:55
URI: http://etheses.whiterose.ac.uk/id/eprint/18185

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