Photoluminescence properties of catalyst-free growth of needle-like ZnO nanowires

Catalyst-free needle-like ZnO nanowires have been grown on Si(111) substrate at 430 °C via a simple solid–vapour process. The obtained nanowires are found to have a uniform size distribution with sharp tips. The lengths of the nanowires range from 2.8 to 3.2 µm with diameters of about 100 nm for the root and 30 nm for the tip parts. The x-ray diffraction (XRD) result shows the nanowires are c -axis preferentially oriented. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) analysis reveal that every single nanowire is a well developed single crystal. The room temperature photoluminescence (PL) spectrum shows a dominant near-band-edge emission peak. The near-band-edge emission is further identified to originate from the radiative free exciton recombination by the temperature-dependent PL.