Fabrication of spherically hierarchical structures with ZnO nanowires synthesized on Au and SiO₂ microspheres

Two kinds of spherically hierarchical structures were fabricated and characterized in this paper. With rough surfaces of high spatial frequency superimposed on sphere surfaces of lower spatial frequency, the surface morphology of spherically hierarchical structures was simulated, and effects of characteristic parameters on the surface morphology were investigated. Au fiber of diameter Φ30 μm was melted from one end for a specific length and cooled down naturally to form an Au microsphere with desirable diameter. ZnO nanowires were hydrothermally synthesized on Au and SiO₂ microspheres respectively, producing two types of spherically hierarchical structures. Based on micrographs of scanning electron microscopy (SEM) and operators of filtration, line edge detection and fitting of MatLab software, roundness errors of Au and SiO₂ microspheres as well as the surface morphology of corresponding spherically hierarchical structures were characterized. Roundness errors of Au microspheres with diameters Φ197 μm and Φ244 μm are 2.51 μm and 4.08 μm respectively, whilst that of SiO₂ microspheres with diameters Φ44.5 μm and Φ50.2 μm are 0.88 μm and 0.98 μm respectively. Values of characteristic parameters of the surface morphology exhibited that non-Gaussian rough surfaces of spherically hierarchical structures were produced. Simulation results were compared with characterization ones, showing the former is in agreement with the latter. The results can be used to batch fabricate spherically hierarchical structures and to construct corresponding sensors in medicine, biology, electrochemistry, and environmental monitoring domains.