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Novel zero-dimensional SnO2(ZnO:Sn)m superlattice nanoparticles were synthesized by a simple method of annealing ZnO nanoparticles precoated with a sol–gel Sn–Zn–O precursor. The annealing temperature and duration were systematically evaluated, and the optimum condition was confirmed as 900 °C for 45 min to obtain ideally fully developed layered structures. Cs-corrected scanning transmission electron microscopy (STEM) revealed that the SnO2(ZnO:Sn)m was composed of alternate stacking of a Sn–O octahedral layer and Sn-doped ZnO slab, which resulted from the anisotropic diffusion of Sn atoms in the ZnO basal plane. A gas sensor based on the SnO2(ZnO:Sn)m superlattice nanoparticles exhibited a superior selectivity towards the poisonous gas of hydrogen sulphide (H2S) among six different types of gases (ethanol, H2, CO, NO2, NH3 and H2S), and an extreme low H2S detection limit of 5 ppb at the working temperature of 400 °C, which was about 3–5 orders lower than that of most ZnO-based H2S gas sensors in the literature. The drastic enhancement of the sensing properties of the SnO2(ZnO:Sn)m superlattice nanoparticles was believed to originate from its unique layered structure, which forms a microcirculation of electrons between the Sn–O atomic layers and Sn-doped ZnO slabs with different work functions, thus greatly accelerating the adsorption and desorption rate of gas molecules and increasing the sensor sensitivity. These new SnO2(ZnO:Sn)m superlattice nanoparticles were demonstrated to be a competitive H2S sensing material candidate for practical application. In addition, the facile superlattice nanoparticles fabrication method presented here could be extended to synthesize other ZnO-based superlattice material systems. [ABSTRACT FROM AUTHOR]

SnO2(ZnO:Sn)m is a new phase recently found in the diagram of a ZnO–SnO2 binary system in the form of a one-dimensional nanowire, which is a new group of superlattice oxide besides the widely known M2O3(ZnO)m (M = trivalent elements, such as In, Ga, and Al, and m = integer). Thereafter, more comprehensive structural and physical properties of SnO2(ZnO:Sn)m are still quite lacking due to the difficulties in high purity synthesis. In this study, we demonstrate a rational design for the growth of SnO2(ZnO:Sn)m superlattice nanowire arrays using a home-built double-tube chemical vapor deposition (CVD) system for the first time. The atomic microstructure of the nanowire array was investigated by Cs-corrected scanning transmission electron microscopy (STEM), and a phenomenon of unsaturated Sn occupation in Sn–O octahedral layers was observed. Two new vibrational modes at 276 cm−1 and 698 cm−1 were found in Raman measurement. The photoluminescence (PL) spectrum of SnO2(ZnO:Sn)m superlattice nanowires displays an interesting broad-spectrum emission in the range of around 380–570 nm. Kelvin probe force microscopy reveals that the average work function of SnO2(ZnO:Sn)m nanowires is in the range of 4.05–4.32 eV. [ABSTRACT FROM AUTHOR]

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 (101̅)Zn2SnO4 (131̅) and SnO2 (020)Zn2SnO4 (11̅1̅), 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. [ABSTRACT FROM AUTHOR]

SnO2(ZnO:Sn)m is a recently reported new phase in the ZnO–SnO2 binary system with a naturally grown superlattice structure, which is currently only found in the form of one-dimensional nanowires. Difficulties in high-purity synthesis and orientation control have hindered further investigations into its potential unique physical properties. Here, we present a novel growth design of fabricating ZnO/SnO2(ZnO:Sn)m binary/superlattice heterojunction nanowire arrays by one-batch chemical vapor deposition to explore the rational growth mechanism of SnO2(ZnO:Sn)m superlattice nanostructures. The morphology, chemical composition and crystal structure of the as-prepared products were characterized by scanning electron microscopy, X-ray diffraction, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy and Cs-corrected scanning transmission electron microscopy. It is revealed that the SnO2(ZnO:Sn)m superlattice section epitaxially grows on top of the ZnO nanowire along the [0001] direction, following the orientation relationships [1̅10]Au//[112̅0]ZnO/SnO2(ZnO:Sn)m and (111)Au//(0002)ZnO/SnO2(ZnO:Sn)m. The Au catalysts on the pre-grown ZnO nanowires play a key role in absorbing further loading of Zn/Sn vapor, inducing the formation of the SnO2(ZnO:Sn)m superlattice on the basal plane of ZnO, at the same time, avoiding the appearance of Sn-rich impurity phases. Photoluminescence measurements display a red shift of the ultraviolet (UV) emission peak from 381 nm to 386 nm and an extra peak at 470 nm, compared with the ZnO reference. This study would shed light on the rational growth of natural oxide superlattice nanowire arrays and complex axial heterojunction nanostructures. [ABSTRACT FROM AUTHOR]