Visible photoassisted room-temperature oxidizing gas-sensing behavior of Sn₂S₃ semiconductor sheets through facile...

Well-crystallized Sn₂S₃ semiconductor thin films with a highly (111)-crystallographic orientation were grown using RF sputtering. The surface morphology of the Sn₂S₃ thin films exhibited a sheet-like feature. The Sn₂S₃ crystallites with a sheet-like surface had a sharp periphery with a thickness in a nanoscale size, and the crystallite size ranged from approximately 150 to 300 nm. Postannealing the as-synthesized Sn₂S₃ thin films further in ambient air at 400 °C engendered roughened and oxidized surfaces on the Sn₂S₃ thin films. Transmission electron microscopy analysis revealed that the surfaces of the Sn₂S₃ thin films transformed into a SnO₂ phase, and well-layered Sn₂S₃-SnO₂ heterostructure thin films were thus formed. The Sn₂S₃-SnO₂ heterostructure thin film exhibited a visible photoassisted room-temperature gas-sensing behavior toward low concentrations of NO₂ gases (0.2-2.5 ppm). By contrast, the pure Sn₂S₃ thin film exhibited an unapparent room-temperature NO₂ gas-sensing behavior under illumination. The suitable band alignment at the interface of the Sn₂S₃-SnO₂ heterostructure thin film and rough surface features might explain the visible photoassisted room-temperature NO₂ gas-sensing responses of the heterostructure thin film on exposure to NO₂ gas at low concentrations in this work.