title: Role of Vacancy Condensation in the Formation of Voids in Rutile TiO2Nanowires.
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 °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.
authors.affiliation: Max-Planck-Institut für Eisenforschung GmbH , Max-Planck-Straße 1, 40237 Düsseldorf, Germany.
authors.forename: Alena
authors.initials: A
authors.lastname: Folger
authors.affiliation: Max-Planck-Institut für Eisenforschung GmbH , Max-Planck-Straße 1, 40237 Düsseldorf, Germany.
authors.forename: Petra
authors.initials: P
authors.lastname: Ebbinghaus
authors.affiliation: Max-Planck-Institut für Eisenforschung GmbH , Max-Planck-Straße 1, 40237 Düsseldorf, Germany.|Department of Materials Science and Engineering, NTNU, Norwegian University of Science and Technology , 7491 Trondheim, Norway.
authors.forename: Andreas
authors.initials: A
authors.lastname: Erbe
authors.affiliation: Max-Planck-Institut für Eisenforschung GmbH , Max-Planck-Straße 1, 40237 Düsseldorf, Germany.|Materials Analytics, RWTH Aachen University , Kopernikusstr. 10, 52074 Aachen, Germany.
authors.forename: Christina
authors.identifier: http://orcid.org/0000-0001-7916-1533
authors.initials: C
authors.lastname: Scheu
keywords: TiO2; nanowire; transmission electron microscopy; vacancy condensation; void