| Summary: | Three dimensional hierarchical metal oxide nanostructures, like TiO2 nanowire
arrays, have attracted great attention for electrochemical energy conversion and storage
applications. The functionality of such devices can be further enhanced by adding a
nanowire shell with a different stoichiometry or composition compared to the core. Here,
we report an approach with a facile heat treatment at 1050 °C, which allows the
fabrication of rutile TiO2–SiOx core-shell nanowire arrays on
silicon substrates. Our detailed electron microscopic investigation shows that this method
is able to cover hydrothermally grown rutile TiO2 nanowires with a uniform
shell of several nanometers in thickness. Moreover, the treatment improves the quality of
the rutile TiO2 core by removing lattice defects, introduced from the
hydrothermal growth. Electron energy loss spectroscopy reveals that the homogeneous shell
around the TiO2 core consists of amorphous SiOx and does not form
any intermediate phase with TiO2 at the interface. Thus, the properties of the
TiO2 core are not affected by the shell, while the shell suppresses undesired
electron back transfer. Latter leads to performance losses in many applications, e.g., dye
sensitized solar cells, and is the main reason for a fast degradation of devices
incorporating organic materials and TiO2.
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