Enhanced photoluminescence of single crystalline ZnO nanotubes in ZnAl2O4 shell

Epitaxial growth of ZnO/ZnAl2O4 (core/shell) nanotubes from Al2O3 coated ZnO nanorods were synthesized using a three-step reaction. In the first step we synthesized ZnO nanorod on Si(100) wafers using chemical vapor deposition, followed by Al2O3 deposition on synthesized ZnO nanorod with the help of atomic-layer deposition. Finally in the last step, the resultant sample (i.e. Al2O3 deposited ZnO nanorod) was calcined at 500 degrees C for 1 h. Hexagonally well-faceted ZnO nanorod arrays were aligned to Si(100) wafers without metal-catalyst at 500 degrees C for 1 h. Thereafter it was transformed to spinel-type ZnAl2O4 nanotubes, which still have ZnO nanotube as a core, by interfacial solid-state reaction in Al2O3 coated ZnO nanorods. XRD and Raman analysis demonstrated that single crystallites of both nanotubes co-exist. The photoluminescence spectra show that ZnO nanorod, Al2O3 coated ZnO nanorod, ZnO/ZnAl2O4 (core/shell) nanotube indicated different luminescence bands with different intensity at He-Cd laser excitation (325 nm line).