Selective growth of ZnO micro- and nano-structures on fs-laser processed metallic Zn substrates for large area applications

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The synthesis of large area micro- and nano-structured ZnO surfaces has been successfully achieved through a two-step process. It involves the irradiation of Zn metal sheets with femtosecond laser pulses (350 fs at 1030nm) at high repetition rates (100 - 500kHz), and fast scanning speeds (cm/s). Subsequently, the irradiated sheets are thermally treated in an Argon flux at 380 oC, a temperature significantly lower than that typically required for growing micro- and nanostructures in ZnO. Fs-laser irradiation promotes the initial development of topography and the localized oxidation of the metal. This enables the further growth of micro- and nanostructures at preferential sites with good crystalline quality and luminescent properties. Analysis of the material at different processing steps shows that the initial laser-induced oxidation is crucial in defining ZnO growth mechanisms upon thermal treatment, and determining the final properties. We have tested the potential use of these structures as reusable photocalyst. The ease of catalyst recovery in photocatalysis experiments and the degree of degradation achieved may be considered as key performance indicators. Photocatalytic activity tests performed with a Rhodamine B solution showed degradation values up to 43% over 90min. The morphology of the samples remains unaltered after photocatalysis experiments.