Abstract
Niobium-doped TiO2 nanotubes were obtained by electrochemical anodization in a 0.5 wt.% NH4F glycerol electrolyte of previously-deposited Nb-doped Ti/TiO2 layers on Si(100) substrates. For film deposition, a DC magnetron sputtering setup was used, with a mosaic target made of metallic Ti and variable numbers of Nb2O5 pellets, placed on the intense sputtering area. By adjusting the number of pellets, we adjusted the dopant concentration in the films. After deposition, both Nb and Ti species were identified in the samples, while after anodization, an increase in the Nb concentration was found, mainly at layer surface.
The nanotube arrays were thermally annealed in air by gradually increasing the temperature between 250 °C and 450 °C, for 45 min. Scanning-electron microscopy images revealed well-formed columnar structures for the three dopant concentrations. While the nanotube diameters varied around 40 nm, the length diminished upon increasing the dopant concentration. Before anodization the samples contained a mixture of metal Ti, titanium dioxide and suboxides (Ti2O3 and TiO) in different concentrations. After anodization and thermal treatment, the Ti4+ oxidation state ocurs in the XPS high resolution spectra, corresponding to the presence of the TiO2 anatase polymorph, exclusively.
No detectable differences exist in the Nb valence state, before and after anodization. The former OH− groups, whose presence was detected in the XPS spectra of the films, are no longer present in the anodized samples.
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This research was supported by the Bilateral Romania – Belarus grant AR-FRBCF-2016.
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Teodorescu-Soare, C.T., Dobromir, M., Stoian, G., Luca, D. (2018). Preparation of Nb-Doped TiO2 Nanotubes Using Magnetron Sputtering. In: Luca, D., Sirghi, L., Costin, C. (eds) Recent Advances in Technology Research and Education. INTER-ACADEMIA 2017. Advances in Intelligent Systems and Computing, vol 660. Springer, Cham. https://doi.org/10.1007/978-3-319-67459-9_25
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