Fabrication, structure and luminescence properties of Al2O3/ZnO coaxial nanowires

Al2O3/ZnO coaxial nanowires were synthesized on (1 0 0) Si substrates by the thermal evaporation of a mixture of Al and TiO2 powders followed by atomic layer deposition of ZnO. Scanning electron microscopy revealed the Al2O3/ZnO coaxial nanowires to have a meandering shape with diameters of a few hundreds of nanometers, lengths of a few tens of micrometers and a ZnO shell layer thicknesses of 8-11 nm. Transmission electron microscopy and X-ray diffraction indicated that the cores and shells of the coaxial nanowires were single crystal rhombohedral-structured α-Al2O3 and polycrystalline wurtzite-structured ZnO, respectively. Al, Zn and O were detected in the energy dispersive X-ray spectrum, indicating that the coaxial nanowires contained almost no contaminants. The photoluminescence measurements showed that the Al2O3 nanowires had two weak emission bands centered at ∼710 nm in the red region ∼340 nm in the near-ultraviolet region. In contrast, Al2O3/ZnO coaxial nanowires had two emission bands: an emission band centered at approximately 570 nm in the yellow region and a weak emission band at approximately 340 nm in the near-ultraviolet region. The yellow emission might have originated from the ZnO shells in the Al2O3/ZnO coaxial nanowires, whereas the weak near-ultraviolet emission might be from the Al2O3 cores in the core-shell nanowires.