The controlling mechanism for determining the growth direction of a Ga-doped ZnO (GaZnO) nanoneedle (NN) by using an Ag nanoparticle (NP) as vapor-liquid-solid (VLS) growth catalyst is disclosed. It is found that the local Ag (111) orientation of the catalytic Ag portion in an Ag NP determines the ZnO (002) orientation of the grown GaZnO and hence the NN growth direction. The ZnO (002) plane of the grown GaZnO is always parallel with the Ag (111) planes of the Ag portions involved in VLS growth in either the top or bottom Ag NP of an NN. When GaN is used as NN growth template, at a sufficiently high temperature (350-450 degrees C), a small Ag NP can become a quasi-single crystal with its Ag (111) plane consistent with the GaN (002) plane and hence results in the growth of a vertical GaZnO NN. However, tilted NNs can be grown from a larger Ag NP or a cluster of Ag NP on GaN due to its non-uniform Ag (111) orientation distribution. At the early stage of GaZnO growth, GaZnO precipitation can be observed between Ag layers within an Ag NP, indicating the growth of a semiconductor on Ag. On other templates, like Si, sapphire, or silicon diode, single-crystal Ag NP cannot be formed such that GaZnO NNs of random orientations are grown.
Yu-Feng Yao, Chi-Ming Weng, Shaobo Yang, Huang-Hui Lin, Chen-Yao Chao, Hao-Tsung Chen, Yean-Woei Kiang, and Chih-Chung Yang, "Growth orientations and crystal structures of ZnO nanoneedles using Ag nanoparticles as catalyst in vapor-liquid-solid growth (Conference Presentation)," Proc. SPIE 10105, Oxide-based Materials and Devices VIII, 101050W (Presented at SPIE OPTO: January 31, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2249541.5393342248001.
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