Figure 2From: Ni-doped TiO2 nanotubes for wide-range hydrogen sensingSEM images of Ni-doped TiO 2 nanotubes. (a) After anodization. (b) Annealed at 525°C. (c) Annealed at 625°C. (d) Cross-section image of the nanotubes annealed at 525°C.Back to article page