Synthesis And Properties Of ZnO Nano/micro-structures By Reducing Agents Of Carbon Group Elements

In recent decades, great interests have been focused on zinc oxide (ZnO) since it has a wide and direct band gap and a large excition binding energy (60meV). ZnO nano/micro-structures have leaded to important applications, for example, in the fields of UV-laser with low threshold, field emission array, surface acoustic wave device, transistor and biosensor.For the synthesis of ZnO nanostructures, thermal evaporation has been widely used. Graphite is generally mixed with ZnO powder to fabricate pure nanostructural ZnO at a temperature of 1000-1100 oC. Due to the introduction of carbon, ZnO precursor (melting point～1490 oC) is reduced and form Zn and ZnOy (evaporated at <500 oC) and subsequently combined with oxygen to synthesize ZnO nanostructures. In this paper, ZnO nano/micro-structures have been formed by thermal evaporation method using ZnO powder mixed with carbon group element (C-diamond, Si, Ge, Sn, or Pb) as the precursor. These new elements are performed as reducing agents as well as the effect of the conventional graphite. In comparison with the conventional synthesis by adding graphite, the heating temperature decreases by 200-300 oC,which is due to stronger reducibility of the new additions. It is essential to thoroughly understand the more new reducing agents to extend the researches on ZnO in numerous application fields. It speculates that the elements in the periodic table that have relatively small ionization energy can be used as new reducing agents.For the cases of ZnO/diamond, ZnO/Si and ZnO/Ge, pure ZnO products were realized. It was found that polycrystalline ZnO films can be achieved near the raw materials at high temperature, while nano-size ZnO products are obtained in the region far away from the heating region. Growth mechanism of ZnO products was investigated. For ZnO/Sn and ZnO/Pb systems, ZnO products generally contain Pb2O3 and Zn2SnO4, respectively, which can be attributed to the low melting point and higher vapor pressures at heating temperature of Sn and Pb. It suggests that at different growth zone, samples with different composition and structure were deposited. Room-temperature photoluminescence (PL) spectroscopy reveals that the Zn2SnO4 phase appearing in the ZnO product can increase the ratio of the intensity of ultraviolet (UV) and defect emission. The UV PL spectrum for the Zn2SnO4-doped ZnO products appears a red shift due to the BGR effect. Magnetization measurements show the saturation magnetizations are higher for the doped ZnO nano/micro-structures compared to pure ZnO samples, indicating there is an increase in the ferromagnetic contribution of Pb2O3 and Zn2SnO4 phases in ZnO nano/micro-structures.