The dissociation of the [a + c] dislocation in GaN
The dissociation of the [a + c] dislocation in GaN
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GaN 中 [a + c] 位错的解离
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
P. Nellist
中科院分区：
文献类型：
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作者：
P. Hirsch;J. Lozano;S. Rhode;Matthew K. Horton;M. Moram;Siyuan Zhang;M. Kappers;C. Humphreys;A. Yasuhara;E. Okunishi;P. Nellist
在1952年，科特雷尔提出，在面心立方晶体中由两个滑移位错相互作用形成的洛默位错可以通过分解成限制堆垛层错的部分位错而转化为不动位错，导致块体进一步滑移，这是加工硬化中的重要概念。衍射对比技术，特别是其“弱光束”变体，提供了这种和许多其他解离的证据，其分辨率极限约为15埃。今天，随着像差校正显微镜的出现，可以直接确定断层和部分位错的原子结构。在本文中，我们描述的研究结果，使用高角度角暗场技术（HAADF）在像差校正的扫描透射电子显微镜（STEM）的（0 0 0 1）GaN薄膜生长在蓝宝石衬底上的[a + c]位错的解离。发现位错相对于c轴倾斜，但光学切片成像方法允许确定结构并估计倾斜角。位错在a平面上通过攀移和滑移解离，STEM结果表明位错的解离反应为[a + c] = 1/2[a + c] + 1/2[a + c] + fault。断层的结构被发现是类似于1965年确定的鼓在氮化铝，但经常修改的步骤，由于扭结的倾斜位错。
In 1952, Cottrell proposed that the Lomer dislocation formed by interaction of two glide dislocations in a fcc crystal could transform into an immobile dislocation by dissociation into partial dislocations bounding a stacking fault, causing a block to further slip, a concept important in work hardening. Evidence for this and many other dissociations has been provided by the diffraction contrast technique and in particular by its ‘weak beam’ variant, which has a resolution limit of about 15 angstroms. Today, with the advent of aberration corrected microscopes it is possible to determine directly the atomic structure of the faults and partial dislocations. In this paper, we describe the results of a study using the High Angle Angular Dark Field technique (HAADF) in an aberration corrected scanning transmission electron microscope (STEM), of the dissociation of the [a + c] dislocations in (0 0 0 1) GaN films grown on sapphire substrates. The dislocations are found to be inclined with respect to the c-axis, but optical sectioning imaging methods allow the structure to be determined and an estimate of the tilt angle to be made. The dislocations are found to be dissociated by climb and glide on the a plane and the STEM results, and structural arguments supported by theoretical calculations suggest that the dissociation reaction is [a + c] = 1/2[a + c] + 1/2[a + c] + fault. The structure of the fault is found to be similar to that identified in 1965 by Drum in AlN but frequently modified by steps due to kinks in the inclined dislocation.