Catalyst-free growth and crystal structures of CdO nanowires and nanotubes

CdO nanowires and nanotubes have been synthesized by the two-step temperature-controlled thermal evaporation process without any catalyst. The results demonstrate that CdO nanowires synthesized by vapor–solid mechanism grow along the [1 1 1] direction and their surface is surrounded by polyhedron-shaped CdO nanocrystals. The formation of nanocrystals should be attributed to the existence of dangling bonds in the sidewall of nanowires. We also successfully synthesized CdO nanotubes and deduced their formation mechanism. The difference of growth orientation for nanotubes and nanowires should be most likely linked to processes of nucleation and growth. Furthermore, energy-dispersive X-ray spectrum and X-ray diffraction analysis also testify that the synthesized nanowires and nanotubes have face-centered cubic CdO structures and possess good crystallinity.