Controlling ZnO nanowire surface density during its growth by altering morphological properties of a ZnO buffer layer by UV laser irradiation

Zinc oxide (ZnO) nanocrystals, which are characterized by their configurations and fine structures, are unique oxide semiconductors. In this report, it is demonstrated that the number density of ZnO nanowires can be controlled by proper treatments of the buffer layer with ultraviolet laser irradiation. ZnO nanowires were synthesized on the locally laser-irradiated ZnO buffer layer using nanoparticle-assisted pulsed-laser deposition (NAPLD). The number density of ZnO nanowires decreased in the region laser-irradiated with <300 mJ/cm², whereas it increased in the region laser-irradiated with more than 400 mJ/cm². Effects of laser irradiation on ZnO buffer layers were investigated by atomic force microscopy, Kelvin probe force microscopy (KPFM), Raman spectroscopy, and X-ray diffraction analyses. In particular, the effects of laser irradiation on the surface work functions of ZnO buffer layers were investigated by KPFM, which is reported for the first time. Additionally, periodically aligned ZnO sub-microcrystals were fabricated as an application of controlling the number density of ZnO nanowires on micropatterned ZnO buffer layers using the four-beam interfered third harmonic of a Nd:YAG laser followed by NAPLD. ZnO sub-microcrystals can be used to fabricate field emitter arrays and can be developed for the application of ZnO nano/microcrystals due to their high throughput.