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Role of Vacancy Condensation in the Formation of Voids in Rutile TiO2 Nanowires

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Folger,  Alena
Nanoanalytics and Interfaces, Independent Max Planck Research Groups, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Ebbinghaus,  Petra
Interface Spectroscopy, Interface Chemistry and Surface Engineering, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Erbe,  Andreas
Interface Spectroscopy, Interface Chemistry and Surface Engineering, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;
Department of Materials Science and Engineering, NTNU - Norwegian University of Science and Technology, 7491 Trondheim, Norway;

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Scheu,  Christina
Nanoanalytics and Interfaces, Independent Max Planck Research Groups, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;
Materials Analytics, RWTH Aachen University, Kopernikusstrasse 10, Aachen, Germany;

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Citation

Folger, A., Ebbinghaus, P., Erbe, A., & Scheu, C. (2017). Role of Vacancy Condensation in the Formation of Voids in Rutile TiO2 Nanowires. ACS Applied Materials and Interfaces, 9(15), 13471-13479. doi:10.1021/acsami.7b01160.


Cite as: http://hdl.handle.net/11858/00-001M-0000-002D-C96C-4
Abstract
Titanium dioxide nanowire (NW) arrays are incorporated in many devices for energy conversion, energy storage, and catalysis. A common approach to fabricate these NWs is based on hydrothermal synthesis strategies. A drawback of this low-temperature method is that the NWs have a high density of defects, such as stacking faults, dislocations; and oxygen vacancies. These defects compromise the performance of devices. Here, we report a postgrowth thermal, annealing procedure to remove these lattice defects and propose a mechanism to explain the underlying changes in the structure of the NWs. A detailed transmission electron microscopy study including in situ observation at elevated temperatures reveals a two-stage process. Additional spectroscopic analyses and X-ray diffraction, experiments clarify the underlying mechanisms. In an early, low-temperature stage, the as-grown mesocrystalline NW converts to a single crystal by the dehydration of surface-bound OH groups. At temperatures above 500 degrees C , condensation of oxygen vacancies takes place, which leads to the fabrication of NWs with internal voids. These voids are faceted and covered with Ti3+-rich amorphous TiOx.