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 degrees 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 mu m 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.