Unveiling hidden epitaxial interfaces in novel SnO2/Zn2SnO4 core–shell nanowires with a multi-domain shield via cross-sectional transmission electron microscopy
Wrapping SnO2 nanowires with appropriate oxide shell materials could produce a significant impact on their photoelectrical and gas sensing performance. In this work, a novel highly crystalline SnO2/Zn2SnO4 core–shell nanowire has been fabricated using a sequential chemical vapor deposition (CVD) method. Cross-sectional transmission electron microscopy (TEM) reveals that the SnO2 core is surrounded by five or six Zn2SnO4 domains, displaying a characteristic quasi-hexagonal cross section. Extensive crystallographic orientation study shows that the growth direction of the core is along the SnO2 [101] direction, parallel to that of the shell Zn2SnO4 [101], i.e. SnO2 [101]∥Zn2SnO4 [101]. While the Zn2SnO4 outer shells have two crystallographic relationships between the SnO2 core, SnO2 (10)∥Zn2SnO4 (13) and SnO2 (020)∥Zn2SnO4 (1), one group of the domains sticks to the SnO2 {111} plane and the other group grows on the SnO2 {020} plane. All the Zn2SnO4 shell domains expose their {111} plane as the ending surface. The tetragonal SnO2 core growing along the [101] direction makes it nearly invisible when collecting electron diffraction from the side view of the core–shell nanowire. The geometrical model deduced from cross-sectional TEM results suggests that there is only one low index zone axis for the core nanowire, i.e. SnO2 [010], along which Moiré fringes and the very rarely seen multiple double-diffraction effect were observed and discussed in detail. We would like to call the attention of researchers to be careful in correlating the microstructure of core–shell nanowires with their physical properties, because merely observing from the radial direction might not be able to reveal the true interface structure.
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