Synthesis, Properties Of The ZnO Thin Films And Nanowhiskers

The technical of the 21st century calls for devices miniaturizing to nano-size, and their ultimate performances should be enhanced markedly. This requirement led to the rapid development of nano-materials. The unique property and the excellent performance of nano-materials lie on their size, surface structure and the interaction between particles. Among the many nano-materials, as a semiconductor material with direct wide band gap (3.37 eV), ZnO have attracted much attention. ZnO is a novelⅡ-Ⅵcompound with low permittivity and high chemical stability and has wide applications in transparent conductive films, SAW devices and gas sensors, etc. In this paper, we mainly discuss the preparation process, microstructure and properties of the ZnO thin films and the ZnO tetrapod nanowhiskers (T-ZnOw).We deposited the ZnO thin film in the pulse laser deposition system (PLD), the high-quality ZnO thin film have been produced by sputtering the low-cost zinc target at the low-temperature. As for the preparation of T-ZnOw, we accomplished them through two steps: Firstly, we prepared the zinc thin films and the ZnO thin film on the sapphire (0001) using PLD system. The characteristics of the vacuum ambience and the rapid deposition speed can prevent the zinc thin films from being oxygenated and polluted during the deposition process. This will be propitious to the study of the growth mechanism. Then, the high-quality and large-scale ZnO tetrapod nanowhiskers are synthesized by the simple thermal evaporation method. The main contents include:1. The property and application of the ZnO thin films and the ZnO tetrapod nanowhiskers have been introduced in detail. We explain the calculational methods of the grain size and the residual stress, which can obtain from the peak of the XRD. Moreover, the grain size and the residual stress of the ZnO thin films have been calculated and explained. The growth mechanism of nano-structured has been a difficult issue in the nano-materials area, we will discuss the growth mechanism in the paper.2. We deposited the ZnO thin film by sputtering the low-cost zinc target, the temperature have an effect on the crystal quality of the ZnO film. The microstructure of the ZnO thin films which are produced at different temperature are investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), FT-IR absorption (FTIR). It demonstrates that the optimal growth temperature of the high-quality ZnO thin film is 300℃. The thin film has the largest grain size, the least residual stress, and the high-quality. The peak of the FTIR absorption depend on the grain size, the large size will conduce the blue shift, contrarily will result in the red shift.3. The Zn films and ZnO films plays an important role on the morphology and microstructure of the T-ZnOw. We prepared the T-ZnOw on Zn films or ZnO films. At the same time, to study the effect of the Zn films and ZnO films on the growth of the ZnO tetrapods, we also made a contrast experiment without them. The morphology and microstructure of the T-ZnOw are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Zn films will make the T-ZnOw grown with the uniform sizes and the high-quality, its arms are prisms with hexagonal cross sections. The ZnO also make the T-ZnOw grown with the uniform sizes and the high-quality, but its arm is cone-shaped. As for the T-ZnOw, which is produced without the Zn films or ZnO films, has low-quality and many other structures are immingled in it. It demonstrates that the Zn films or ZnO films will make the T-ZnOw grown with the different growth mechanism, therefore we obtain the T-ZnOw with unlike morphology and microstructure.4. We study the effect of the gas saturation on the T-ZnOw through adding the quantity of the zinc powder. The morphology and microstructure of the T-ZnOw are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The high gas saturation will make the atom been caught easily by the side of the whisker, which can make for the side growth and result in the leafy arms of the T-ZnOw.5. The PL spectrum of the T-ZnOw which is produced with the Zn film is measured. Two distinct emissions can be observed: a strong ultraviolet (UV) emission band centered at 394 nm and a weak green emission band centered at 518 nm. Compare with the band gap of bulk ZnO (around 380 nm), the UV emission centered at 394 nm appears a red shift. The reason has been discussed in the paper.