Visible photoassisted room-temperature oxidizing gas-sensing behavior of SnS semiconductor sheets through facile thermal annealing.

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