Solution grown ultra-violet emitting quasi-aligned ZnO nanotubes.

Quasi-aligned ZnO nanotubes were grown in a high density on Si substrate via aqueous solution method at low temperature of 65 degrees C by using zinc nitrate and hexamethylenetetramine. The detailed structural characterizations revealed that the as-synthesized nanotubes are single-crystalline possessing a hexagonal phase and grown along the [0001] direction. Raman-scattering spectrum exhibits a strong and sharp optical-phonon E2 high-mode at 437 cm(-1) again confirming the good crystal quality with hexagonal crystal structure for the as-synthesized nanotubes. A strong ultraviolet (UV) emission with a weak and broad orange is observed from the room-temperature photoluminescence (PL) spectrum which substantiates the good optical properties for the as-grown nanotubes. The detailed growth mechanism has also been proposed for the formation of as-grown nanotubes based on chemical reactions involved and different crystallographic habits of wurtzite hexagonal ZnO.