Study Of Micro/Nanostructured ZrO₂ Fabricated By Photo-assisted MOCVD

Zr O₂ is a kind of oxide materials with very stable chemical and physical properties.It is reported that Zr O₂ nanostructures have already been used as artificial pinning centers to strongly improve the critical current density of high temperature superconductors YBCO bulk material. At present, our group has gained the ability to prepare high quality YBCO film by photo-assisted MOCVD technique, and our new goal is to improve further the critical current density of superconducting thin films.Therefore, how to control the growth of Zr O₂ on the LAO（100） substrate is very essential. For these reasons, this paper introduces the study on the controlled growth of Zr O₂ nano and micron structures on the LAO substrate at first. On the other hand,recent studies show that nano Zr O₂ has been widely used in catalysis, LED encapsulations and many other fields, so the relationship between growth parameters and surface morphologies of Zr O₂ nanodots on Si substrate is also investigated. The main contents are as follows:（1） This part is about the influence of growth parameters on the morphology of Zr O₂ on LAO（100） substrate. The experimental results show that there are two kinds of completely different surface morphologies（i.e.Zr O₂ nanodots and microwires） on the substrate. Growth parameters include growth temperature, growth time and oxygen partial pressure. It is found that in the process of modulating growth parameters there is an obvious competitive relationship between the nanodots and microwires. When the growth temperature is low, the nanodots are characterized by large and sparse ones;with the temperature increasing, the nanodots start to appear as small and dense; but when the growth temperature is increased further, the nanodots become large and sparse again. However, in the process of modulating growth temperature, the trend of microwires is totally different. In addition, experimental results show there is also a competitive relationship between two kind of different morphologies in the process of modulating growth time and oxygen partial pressure. With the increase of oxygenpartial pressure or growth time, the growth of microwires tends to be dominant compared with nanodots.（2） On the other hand, the experimental results show that the controllable growth of Zr O₂ nanodots is completely feasible on Si（100） substrate and Si（111） substrate.With growth temperature increasing, the density of nanodots on Si（100） substrate gradually become lower while their sizes become larger, and the nanodots on Si（111）substrate achieve a transition from clusters growth to island growth. In addition, in the process of increasing growth time, the size of Zr O₂ nanodots on Si（111） substrate becomes larger and larger; meanwhile, due to the low lattice mismatch, Zr O₂ films have been formed on Si（111） substrate. And partial pressure of oxygen is also essential for the morphology of nanodots. With high oxygen partial pressure, Zr O₂ nanodots on Si（100） substrate prefer island growth, and the morphologies of nanodots on Si（111） substrate are characterized by small and dense ones.