Visible photoassisted room-temperature oxidizing gas-sensing behavior of Sn(2)S(3) semiconductor sheets through facile thermal annealing

Well-crystallized Sn(2)S(3) semiconductor thin films with a highly (111)-crystallographic orientation were grown using RF sputtering. The surface morphology of the Sn(2)S(3) thin films exhibited a sheet-like feature. The Sn(2)S(3) 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 Sn(2)S(3) thin films further in ambient air at 400 °C engendered roughened and oxidized surfaces on the Sn(2)S(3) thin films. Transmission electron microscopy analysis revealed that the surfaces of the Sn(2)S(3) thin films transformed into a SnO(2) phase, and well-layered Sn(2)S(3)–SnO(2) heterostructure thin films were thus formed. The Sn(2)S(3)–SnO(2) heterostructure thin film exhibited a visible photoassisted room-temperature gas-sensing behavior toward low concentrations of NO(2) gases (0.2–2.5 ppm). By contrast, the pure Sn(2)S(3) thin film exhibited an unapparent room-temperature NO(2) gas-sensing behavior under illumination. The suitable band alignment at the interface of the Sn(2)S(3)–SnO(2) heterostructure thin film and rough surface features might explain the visible photoassisted room-temperature NO(2) gas-sensing responses of the heterostructure thin film on exposure to NO(2) gas at low concentrations in this work.