Figure 4.

TEM images of CuO nanowires and nanotubes obtained by annealing at 650°C for varying periods of time: (a) 1 h, (b) 4 h, (c) 10 h, and (d) 20 h. The scale bars in (a-d) are 20 nm. (e) Schematic illustration of the growth process of CuO nanotubes.