Enhanced properties of hierarchically-nanostructured undoped acceptor-rich ZnO single-crystal microtube irradiated by UV laser

Here a variety of hierarchic nanostructures on the undoped acceptor-rich ZnO (A-ZnO) single-crystal microtube are fabricated by KrF excimer laser irradiation. The effects of process parameters, i.e. laser fluence and number of pulse (NOP), on nanostructure morphology of the A-ZnO microtube are investigated, by which the controllable hierarchic nanostructures are achieved. The mechanism of the nanostructure formation is attributed to self-assembled growth by decomposition and re-nucleation owing to rapid heating and cooling down during laser irradiation near Zn-vacancy-related point defects. The Raman and photoluminescence spectra confirm that the nanostructures possess massive surface defects, e.g. oxygen vacancies (VO) and zinc interstitials (Zni). The electrical resistivity of the nanostructured A-ZnO microtube is down to ∼10−3 Ω cm, about one order of magnitude lower than that of the as-grown A-ZnO microtube. The great ratio of surface area to volume of the nanostructures realizes the improved UV detection and photodegradation performance. The optimal photoresponsivity can be up to 27.08 A/W using the process parameters of 200 mJ/cm2 and 100 pulses. The catalytic degradation rate of the A-ZnO microtube irradiated by 150 mJ/cm2 and 200 pulses with 6-nm Au nanoparticles decoration for methylene blue solution is ∼3.4 times higher than the commercial nanoparticles. The present work paves a new way to design and fabricate a variety of hierarchic nanostructures on undoped A-ZnO microtube for enhanced electrical and photocatalytic performance.