Oxidizing agent impacting on growth of ZnO tetrapod nanostructures and its characterization

In this paper, the fabrication of ZnO tetrapod was investigated. It was synthesized by the thermal oxidation technique using metal zinc powder mixed with oxidizing agents such as hydrogen peroxide (H₂O₂) and ammonium persulfate ((NH₄)₂S₂O₈). The furnace heating temperature reached at 1000 °C in the air. The average diameter and length of a tetrapod leg for mixture with H₂O₂ from SEM were 45.3 nm and 1.57 μm, respectively. The oxygen vacancy (36%) of ZnO tetrapod with H₂O₂ was higher than 33% of ZnO tetrapod with only Zn. Growth mechanism of ZnO tetrapod was processed via the formation of Zn nucleus and growing the wurtzite structure. The growing directions of ZnO crystal conformed with the [0001] direction. ZnO tetrapod showed up the high resolution TEM image with the lattice spacing 0.252 nm. From these results, this work was indicated that H₂O₂ solution was a better oxidizing reaction helper to make ZnO tetrapod nanostructures than anything else.

Photoluminescence of ZnO Nanowires: A Review

One-dimensional ZnO nanostructures (nanowires/nanorods) are attractive materials for applications such as gas sensors, biosensors, solar cells, and photocatalysts. This is due to the relatively easy production process of these kinds of nanostructures with excellent charge carrier transport properties and high crystalline quality. In this work, we review the photoluminescence (PL) properties of single and collective ZnO nanowires and nanorods. As different growth techniques were obtained for the presented samples, a brief review of two popular growth methods, vapor-liquid-solid (VLS) and hydrothermal, is shown. Then, a discussion of the emission process and characteristics of the near-band edge excitonic emission (NBE) and deep-level emission (DLE) bands is presented. Their respective contribution to the total emission of the nanostructure is discussed using the spatial information distribution obtained by scanning transmission electron microscopy−cathodoluminescence (STEM-CL) measurements. Also, the influence of surface effects on the photoluminescence of ZnO nanowires, as well as the temperature dependence, is briefly discussed for both ultraviolet and visible emissions. Finally, we present a discussion of the size reduction effects of the two main photoluminescent bands of ZnO. For a wide emission (near ultra-violet and visible), which has sometimes been attributed to different origins, we present a summary of the different native point defects or trap centers in ZnO as a cause for the different deep-level emission bands.