Fabrication and optical absorption of size-tunable core-shell structured ZnO nanotube-CdTe arrays

Core-shell structured ZnO nanotube-CdTe nanocomposite arrays have been synthesized by one-step thermal evaporation of CdTe on single-crystalline ZnO nanotube arrays, which are on the ITO glass. The CdTe nanocrystal shells can be formed both at the inner and outer side of the ZnO nanotubes. It is found that the shell thickness is about 100 nm for the ZnO nanotubes with an average 250 nm in diameter and 12 nm in wall thickness. The selective nucleation and growth of the CdTe nanocrystals plays an important role in the formation of the core-shell structure. The inner diameter of ZnO nanotubes has an obvious influence on the product morphology. For smaller inner diameter (such as 150 nm), CdTe nanoclusters will form randomly irrespective of the nanotubes. While thicker CdTe shells with thickness up to ~500 nm can be obtained for larger inner diameter (~600 nm). The absorption of visible light within 826 nm was found to increase linearly with the increasing of the shell thickness for the core-shell nanocomposite arrays. This was attributed to the increased amount ratio of CdTe to ZnO in the composite nanostructure.