Fabrication And Photoelectric Applications Of Hierarchically-Nanostructured Undoped Acceptor-Rich ZnO Single-Crystal Microtube Irradiated By UV Laser

ZnO has attracted considerable attention due to its extraordinary optical and electrical properties in past decades to explore the feasibility for highly efficient and stable UV LEDs/LDs,solar cells,field-effect transistors,etc.The ZnO microtube with hexagonal cross section is an optical microcavity supporting multiple resonant modes.The acceptor-rich ZnO?A-ZnO?microtubes were prepared by optical vapor supersaturated precipitation?OVSP?in our previous work.Several interesting phenomena of the A-ZnO microtube has demonstrated in our previous study,e.g.temperature-sensitive multicolor luminescence,ultralow-threshold UV lasing,and enhanced photocatalytic degradation.As an instantaneous high-density and controllable energy source,laser has been widely used in high-efficient modification of semiconductor properties.Here a variety of hierarchic nanostructures on the undoped A-ZnO single-crystal microtube prepared by OVSP are fabricated by 248-nm 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.Six typical types of hierarchic nanostructures are achieved.The mechanism of the nanostructure formation is attributed to the thermal effect of laser irradiation and abundant V_Zn-related stable acceptors with high concentration in ZnO microtubes.The low fluence guaranteed the surface temperature is higher than the decomposition temperature.The self-assembled growth by decomposition and re-nucleation occurred to form a variety of nanostructures owing to rapid heating and cooling down during laser irradiation near Zn-vacancy-related point defects.The laser fluence determined the morphology of the hierarchic nanostructures critically due to the higher temperature caused by greater fluence,whereas the size and density of the nanostructures are governed by the NOP.The Raman and photoluminescence spectra confirm that the nanostructures possess massive surface defects,e.g.oxygen vacancies?V_O?and zinc interstitials?Zn_i?.The electrical resistivity of the nanostructured A-ZnO microtube is down to 3.39×10^-3?·cm using 200 mJ/cm² and 300 pulses,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 of200 mJ/cm² and 100 pulses.The responsivity is 8-fold enhancement and the response time is reduced by 75% compared with the as-grown A-ZnO microtube.The maximum responsivity is up to 50 and 270 times greater than that of ZnO single-crystal and thin film,respectively.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 good recycling performance is beneficial to practical usage as well as compatible to micro-fluidic channels.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.