Structural- and optical-property characterization of three-dimensional branched ZnO nanospikes

Current study reports the synthesis of three-dimensional (3-D) ZnO nanospikes with anomalous optical property, where zinc stearate is adopted as a safe, common and low-cost precursor that undergoes thermal pyrolysis under non-hydrolytic approach. High resolution transmission electron microscope (HRTEM) and scanning electron microscope (SEM) result show that the as-synthesized 3-D ZnO nanospikes are constructed by bundle of nanorods that sprout radially outwards in random orientation. The possible growth mechanism is discussed by referring to the microscopy results. X-ray diffraction (XRD) pattern confirms that the nanospikes are highly crystalline, which existed in hexagonal wurtzite crystal structure. Optical absorption characterization shows that the onset absorption for the nanospikes is slightly red-shifted if compared to commercial ZnO and the corresponding bandgap energy is estimated to be 3.1 eV. The photoluminescene (PL) result of ZnO nanospikes indicate that its optical emission exhibits weak UV emission but very intense visible-light emission that ranged from green- up to red-region. The factors that contributed to the intriguing PL characteristic are discussed. Current finding would offer a versatile synthesis scheme in engineering advanced nanostructures with new design that exhibit congruent optical property. - Graphical abstract: Display Omitted - Highlights: • Pyrolysis of zinc stearate in synthesizing 3-D ZnO nanospikes • ZnO nanospikes possess bundle of nanorods that sprout out from the hexagonal stump • Growth mechanism is deduced to elucidate the morphological evolution from nanobullet to nanospike with branching topology • PL spectrum indicate that the nanospike exhibit prominent visible-light emission that ranged from green- to red-region