Growth mechanism of ZnO nanostructures produced by ultraviolet and visible laser ablation

ZnO nanostructures were fabricated on noble-metal (Au-Ag alloy) coated substrates by pulsed laser deposition. We studied the influence of the laser wavelength used for ablation on the morphology, growth mechanism, and optical properties of the nanostructures. ZnO nanostructures produced by UV (355 nm) pulsed laser deposition possessed a mixed-structures morphology, composed of nanorods (mean diameter of 25-50 nm) and large-size nanobelts. The density of these structures could be controlled by varying the Au/Ag ratio in the alloy layer. Samples deposited by pulsed laser deposition at VIS wavelength (532 nm), instead, presented a dense agglomeration of nanoparticles (nanorods) with a mean diameter in the range of 40-55 nm. The growth of the ZnO nanostructures followed a vapor-solid or vapor-liquid-solid mechanism depending on the catalyst layer composition when a UV source was used for ablation. The presence of Au and Ag on the ZnO surface was a clear indication for a vapor-liquid-solid mechanism of growth for nanostructures deposited by using a VIS radiation. A narrow peak centered at 379 nm in UV band and a broadband visible emission with a peak at 540 nm were observed in all nanostructures. The UV-deposited sample exhibited a stronger UV emission, while the visible emission was predominant for the sample deposited by VIS ablation. (C) 2017 Elsevier B.V. All rights reserved.