Improving the seed layer and controlling the size and growth orientation of ZnO micro/nanorod arrays by hydrothermal method
Date Issued
2010
Date
2010
Author(s)
Lin, Wen-Han
Abstract
The study of this thesis is to investigate how to apply the hydrothermal method to fabricate well-oriented and high-quality zinc oxide micro/nanorods. First, we introduce how to obtain the ZnO thin films prepared by sol-gel method and hydrothermally prepared ZnO micro/nanorods. Then we discussed the effects of annealing process on ZnO thin films and ZnO nanorods. After that, we pre-coated a gold thin film on ZnO thin film before annealing and successfully improved the orientation and size of ZnO micro/nanorods. Finally, we discussed the change of the existing LED structure, and to grow ZnO micro/nanorods on GaN substrate and approached selected growth.
Through the experiment, we find that the ZnO thin film can form bigger ZnO crystal when annealed at around 900°C. In order to grow a large ZnO rod, ZnO sol-gel thin film has to anneal at high temperatures to form a big grain. At the same time, the big grain causes random growth of nanorods. In this work, we demonstrate a new method by annealing a pre-coated thin metal film on a ZnO sol-gel seed layer to obtain a smooth seed layer to grow vertical, well-aligned, and large ZnO rods. We also do the XRD analysis, the peaks in the x-ray diffraction patterns are indexed to the hexagonal phase of ZnO. With the gold-coating treatment, only a very strong (002) diffraction peak is observed, indicating that the ZnO sample has a high c-axis orientation. The PL spectrum of the ZnO nanorods shows the intensity of the green emission for the ZnO rods on the seed layer with pre-coated gold treatment was much weaker than that of the ZnO rods on the normal ZnO seed layer. It shows that the ZnO rods on the smooth seed layer have a better crystallization than the others. The EDS spectra reveal the presence of Zn and O elements, confirming that there is no residual gold on the sample and that the nanowire arrays are primarily ZnO.
The function of coating a thin metal film on a sol-gel ZnO-seed-coated substrate by using an E-gun before doing the annealing treatment is to inhibit the formation of ZnO crystals and let the crystallization occur along the x-y plane instead of growing along the c-axis direction during the annealing process. Next, the smooth seed layer also grows the ZnO nanorods through a hydrothermal method. We see the ZnO nanorods with good orientation along the c-axis and improved rod size and the lateral rod size is about 200~400nm and the rod length is up to 1830nm.
Subjects
Hydrothermal
ZnO micro/nanorods
ZnO thin films
sol-gel method
annealing
Type
thesis
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