Controllable growth of single crystalline CdS nanotubes by thermal evaporation

• It is the first time to synthesize single crystalline wurtzite CdS nanotubes by controllable, and reproducible thermal evaporation of CdS powder.
• The TEM results demonstrate that the CdS nanotubes are single crystalline and grow along the [0 0 0 1] direction.
• The growth mechanism has been proposed for the CdS nanotubes.
• The nanotubes with a low density of defects can be produced, and only free-exciton-related emission peaks are observed in their PL spectra.

CdS nanotubes have been successfully prepared by thermal evaporation of CdS powder. The TEM measurements demonstrate that the CdS nanotubes are single crystalline wurtzite and grow along the [0 0 0 1] direction. The nanotubes nucleate and grow from catalytic Au islands on a silicon substrate, with both their diameter and morphology dependent on size of catalyst islands. A model is presented to explain the nucleation and growth of nanotubes. By optimizing their diameter and morphology, the CdS nanotubes with high optical quality were obtained, and only free-exciton-related emission peaks are observed in their PL spectra.