Fabrication of coaxial nanowire heterostructures: SiO x nanowires with conformal TiO2 coatings
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Silica nanowires, grown via the active oxidation of a silicon substrate, have been coated with TiO2 using two coating methods: solution-based deposition of Ti-alkoxides and atomic layer deposition. Analysis of as-deposited and annealed films shows that it is possible to produce stable conformal coatings of either the anatase or rutile phases of TiO2 on nanowires with diameters greater than 100 nm when annealed between 500–600°C and 800–900°C, respectively, with annealing at higher temperatures (1050°C) producing coatings with a highly facetted rutile morphology. The efficacy of the process is shown to depend on nanowire diameter, with nanowires having diameters less than about 100 nm fusing together during solution-based coating and decomposing during TiO2 atomic layer deposition. The use of a suitable buffer layer is shown to be an effective means of minimizing nanowire decomposition. Finally, annealing coated nanowires under active oxidation conditions (1100°C) is shown to be an effective technique for depositing additional conformal SiO x coatings, thereby providing a means of fabricating multi-layered coaxial nanostructures.
KeywordsTiO2 HfO2 Atomic Layer Deposition Rutile Phase Atomic Layer Deposition Coating
The Australian Research Council is gratefully acknowledged for financial support. The ANU nodes of the ANFF and The AMMRF, both established under the Australian National Cooperative Research Infrastructure Strategy, are acknowledged for access to the facilities used in this work.
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