Substitutional nitrogen-doped tin oxide single crystalline submicrorod arrays: Vertical growth, band gap tuning and visible light-driven photocatalysis

High-density substitutional N-doped SnO₂ submicrorod arrays were grown on Si and quartz substrates by catalysts-free reactive sputtering. Scanning electron microscope and high-resolution transmission electron microscopy results show that the submicrorods are vertically aligned single crystal with quasi-tetrahedral pyramid shape nanotip at the top end. The density and the shape of the submicrorods can be modulated by the nitrogen partial pressure. Ellipsometry and optical absorption characterization show that after substitutional N-doping, the band gap of N-doped SnO₂ submicrorod shifts toward visible light region (up to 624 nm), and the visible light absorption are significantly enhanced due to the band gap narrowing. The photodegradation of methylene blue by N-doped SnO₂ submicrorod under visible light illumination is demonstrated, and it was found that the surface-to-volume ratio plays an important role in achieving high photocatalytic reactivity. The SnO₂:N submicrorod arrays with visible light band gap may have potential applications in solar cells electrode and visible light sensitive photocatalyst.