Interfacial atomistics and bonding involved in gold-mediated growth of rutile nanostructures

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Lin, Minghui
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One-dimensional oxide nanostructures such as nanowires have received great attention as potential candidates for the construction of nanoscale electronic and catalytic devices because of their unique physical properties. In seed-mediated growth of oxide nanostructures, seed/oxide interfaces are essential in guiding directional growth of oxides under the seeds and require further investigation. The aim of this thesis is to study the seed/oxide interface involved in seed-mediated growth of oxide nanostructures in order to develop a better understanding of oxide growth. We selected Au/TiO2 as the understudied system because TiO2 nanowires have important applications in photoelectrochemical water splitting and solar cells. A systematic investigation was performed on three types of interfaces including their crystallographic orientations, atomic structure, and local bonding environment. The Au/TiO2 interfaces, including the interface between dewetted Au particles and TiO2 single crystal substrates, and the interface between Au seeds and TiO2 nanowires, were investigated using X-ray diffraction and atomic-resolved scanning transmission electron microscope. Interface orientation relationships between Au seeds and TiO2 nanowires, identified from selected area electron diffraction are consistent with those discovered in dewetted Au particles on TiO2 single crystal substrates. New irrational orientation relationships were identified and were found to be promoted at temperature >800 ℃. According to their lattice structures, geometrical models, such as coincidence site lattice (CSL) and constrained coincidence site lattice (CCSL) theories, predicted the occurrence of these irrational orientation relationships with the aid of constrained lattices. These orientation relationships corresponded to various atomic structures from atomic-flat interface to significant interface reconstructions. Another interface is the interface between an TiOx overlay and Au seed. A TiOx lay with a thickness of 1-2 nm was detected on the surface of Au seeds and proved to be essential for the growth of TiO2 nanowires. The local environment of Au at Au-TiOx interface was further investigated with X-ray absorption spectroscopy. Au L3-edge spectra indicated Au-Au and Au-Ti bonding present at the interface, showing bonding length characteristics of Au/TiO2 interface.
Gold-rutile interface, Nanowire growth, VLS