纳米棒
材料科学
蓝宝石
外延
异质结
化学气相沉积
透射电子显微镜
聚结(物理)
光电子学
位错
晶界
纳米技术
图层(电子)
复合材料
光学
激光器
微观结构
物理
天体生物学
作者
Yuekui Sun,D. Cherns,Rachel P. Doherty,James Warren,Peter J Heard
摘要
Transmission electron microscopy was used to study threading dislocations (TDs) in epitaxial ZnO films on (0001) sapphire substrates produced by a two-step method. First, ZnO was deposited by pulsed laser deposition. It was found that the sample consisted of a continuous buffer layer with a high density, 7×1010/cm2, of TDs, with c-aligned nanorods on its top. The nanorods revealed few, if any, TDs. A further layer of ZnO was then grown under conditions favoring nanorod growth, using either chemical vapor deposition (CVD) or a hydrothermal method. In both cases the nanorods grew laterally and eventually coalesced to form a continuous overgrowth. The nanorods remained mostly free of dislocations until coalescence. New grain boundary dislocations were generated where nanorods coalesced, but many of these dislocations migrated laterally and interacted with other dislocations to form closed loops. The TD density at the top of the continuous film was thereby reduced to 1×109/cm2 and 7×109/cm2 in the cases of hydrothermal and CVD treatments, respectively. The mechanism of growth and the means by which TDs are reduced are explained.
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