Fig. 2.

SEM and TEM images and XRD patterns of SnO₂ nanotube arrays and SnO₂-TiO₂ nanomace arrays. a High-magnification top-view SEM image of SnO₂ nanotube arrays. b SEM image of 6-h-grown STNMAs. c SEM image of 12-h-grown STNMAs. d SEM image of 18-h-grown STNMAs. e SEM image of 24-h-grown STNMAs. f X-ray diffraction patterns of the substrate, SnO₂ nanotube arrays, and STNMAs. g TEM image of bare SNA. h TEM image of 18-h-grown STNMAs