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Title
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Three-dimensional characterisation of nanomaterials : from model-like systems to real nanostructures
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Author
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Abstract
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| Nanomaterials have attracted enormous attention during the last decades due to their unique physical properties (e.g. optical, thermal, electronic and catalytic properties). This is of importance for an increasing range of applications of nanomaterials, where the characterisation techniques are vital to understand the relationship between their morphology, size, composition or crystallinity and their physical properties. Recent advances in (scanning) transmission electron microscopy ((S)TEM) have enabled a comprehensive characterisation of the chemical composition, size and crystallinity of nanomaterials, from the nanoscale to the atomic level. Nevertheless, images obtained with (S)TEM only correspond to a two-dimensional (2D) projection of a three-dimensional (3D) object, hindering the quantification and interpretation of the material’s shape. To unravel the structure-properties relationship, electron tomography is required. Electron tomography has become an important technique to investigate nanomaterials, but only relatively simple structures (e.g., model-like materials like monocrystalline nanospheres and nanorods) can be investigated in a routinely manner. During my PhD research, I applied advanced techniques for electron tomography for the investigation of complex nanostructures, such as nanoparticles containing structural defects and beam sensitive nanomaterials. Advanced techniques for electron microscopy were employed for the identification of the defect type as well as the statistical distribution of nanoparticles containing such structural defects. Moreover, an approach for the 3D atomic structure recovery that was recently developed in our laboratory was used for the investigation of different systems containing unknown defects, which prevents the use of any prior information regarding the object under investigation during the tomographic reconstruction. By a thorough characterization of defects at the atomic level (e.g., grain boundaries/dislocations in welded nanorods) in combination with spectroscopic techniques, a better understanding on the relationship of optical properties and crystallinity was achieved. Additionally, the formation mechanisms of hollow nanoparticles induced by ultrafast laser pulses was unveiled by combining advanced approaches for the atomic structure characterization in 3D, methods for the determination of the chemical composition of nanoparticles and techniques for investigation of the dynamical behaviour of nanoparticles in 3D under increasing temperature conditions in in-situ environment. Still, due to the sensitiveness of some nanostructures towards the electron beam, structural modifications can be induced in the nanomaterials during the investigations by electron microscopy, preventing the establishment of a structure-to-properties relationship. Therefore, advanced approaches for the 3D characterization of beam sensitive structures were employed, at the nano and atomic levels. |
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Language
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English
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Publication
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Antwerpen
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Universiteit Antwerpen, Faculteit Wetenschappen, Departement Fysica
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2020
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Volume/pages
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230 p.
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Note
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Bals, S. [Supervisor]
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Full text (open access)
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