Epitaxial TiO 2/SnO 2 core-shell heterostructure by atomic layer deposition

Abstract
Taking TiO 2/SnO 2 core-shell nanowires (NWs) as a model system, we systematically investigate the structure and the morphological evolution of this heterostructure synthesized by atomic layer deposition/epitaxy (ALD/ALE). All characterizations, by X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction and Raman spectra, reveal that single crystalline rutile TiO 2 shells can be epitaxially grown on SnO 2 NWs with an atomically sharp interface at low temperature (250 °C). The growth behavior of the TiO 2 shells highly depends on the surface orientations and the geometrical shape of the core SnO 2 NW cross-section. Atomically smooth surfaces are found for growth on the {110} surface. Rough surfaces develop on {100} surfaces due to (100) - (1 × 3) reconstruction, by introducing steps in the [010] direction as a continuation of {110} facets. Lattice mismatch induces superlattice structures in the TiO 2 shell and misfit dislocations along the interface. Conformal epitaxial growth has been observed for SnO 2 NW cores with an octagonal cross-section ({100} and {110} surfaces). However, for a rectangular core ({101} and {010} surfaces), the shell also derives an octagonal shape from the epitaxial growth, which was explained by a proposed model based on ALD kinetics. The surface steps and defects induced by the lattice mismatch likely lead to improved photoluminescence (PL) performance for the yellow emission. Compared to the pure SnO 2 NWs, the PL spectrum of the core-shell nanostructures exhibits a stronger emission peak, which suggests potential applications in optoelectronics. © The Royal Society of Chemistry 2012.

Citation
Nie, A., Liu, J., Li, Q., Cheng, Y., Dong, C., Zhou, W., … Wang, H. (2012). Epitaxial TiO2/SnO2 core–shell heterostructure by atomic layer deposition. Journal of Materials Chemistry, 22(21), 10665. doi:10.1039/c2jm30690e

Acknowledgements
This work has been supported by the National Science Foundation of China (Grant No. 11002124 and No. 11090333) and the Science Foundation of Chinese University (Grant No. 2011QNA4038).

Publisher
Royal Society of Chemistry (RSC)

Journal
Journal of Materials Chemistry

DOI
10.1039/c2jm30690e

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