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.
Jianing Tan,Song Jiang,Binghui Ge,Bojia Xu,Baobao Cao
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.
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