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Highlights • A new type NiO decorated SnO 2 vertical-standing nanotubes composite thin film was synthesized via a facile hydrothermal method. • Numerous SnO 2 vertical-standing nanotubes with the size of 200–300 nm in diameter and 1.5 μm in length formed a porous microstructure. • NiO nanoplates with the size of 20 nm in diameter decorated on the inside or outside surface of SnO 2 nanotubes formed a heterojunction structure. • The NiO/SnO 2 thin film gas sensor with an Ni2+/Sn4+ molar ratio of 5% exhibited excellent response characteristics to ethanol at 250 ℃. Abstract In this work, a new type NiO decorated SnO 2 vertical-standing nanotubes composite thin film was synthesized successfully via a facile hydrothermal method. The microstructure, physico-chemical surface state and morphology of the composite thin film were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), respectively. The results showed that the NiO decorated SnO 2 vertical-standing nanotubes composite thin film with a coral-like microstructure was built of numerous 1D SnO 2 nanotubes with the size of 200–300 nm in diameter and 1.5 μm in length; while NiO nanoplates with the size of 20 nm in diameter decorated on the surface of SnO 2 nanotubes. Due to the enhanced adsorption of oxygen molecules, formation of p -NiO/ n -SnO 2 heterojunction and porous structure, the NiO/SnO 2 thin film gas sensor with an Ni2+/Sn4+ molar ratio of 5% exhibited high response value, good selectivity and quick response characteristics to ethanol at the optimum working temperature of 250 ℃. [ABSTRACT FROM AUTHOR]

The antimony-doped tin oxide thin films for gas sensors were prepared via a sol–gel route on alumina substrates. The influence of the antimony addition amount on the electrical resistance of thin films was concluded. The relationship between them was plotted in the coordinates of logarithmic resistance against doping amount. On the basis of the Schottky barrier model, a novel method was used to evaluate the width of depletion layer of semiconductive gas sensors by using the first-order derivative of logarithmic resistance with respect to doping amount. The values of the depletion layer width were calculated for the antimony-doped thin films. The H 2 S gas was used to examine the sensor properties, which positively correlated to the depletion layer width. The oxygen species of O 2− and O − were determined to be the adsorbates on SnO 2 grains with the same proportion at the operating temperature of 300 °C. The location of the Fermi level was found to be a crucial factor that dominated the calculation results. [ABSTRACT FROM AUTHOR]