Atomically-resolved mappings of the indium composition in InGaN/GaN multi-quantum well structures have been obtained by quantifying the contrast in HAADF-STEM. The quantification procedure presented here does not rely on computation-intensive simulations, but rather uses EDX measurements to calibrate the HAADF-STEM contrast. The histogram of indium compositions obtained from the mapping provides unique insights into the growth of InGaN: the transition from GaN to InGaN and vice versa occurs in discreet increments of composition; each increment corresponds to one monolayer of the interface, indicating that nucleation takes longer than the lateral growth of the step. Strain-state analysis is also performed by applying Peak-Pair Analysis to the positions of the atomic columns identified the quantification of the contrast. The strain mappings yield an estimate of the composition in good agreement with the one obtained from quantified HAADF-STEM, albeit with a lower precision. Possible improvements to increase the precision of the strain mappings are discussed, opening potential pathways for the quantification of arbitrary quaternary alloys at atomic scales.

中文翻译：

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使用 EDX 对原子分辨的 HAADF-STEM 图像进行实验量化

通过量化 HAADF-STEM 中的对比度，已经获得了 InGaN/GaN 多量子阱结构中铟成分的原子分辨映射。此处介绍的量化程序不依赖于计算密集型模拟，而是使用 EDX 测量来校准 HAADF-STEM 对比度。从映射中获得的铟成分直方图提供了对 InGaN 生长的独特见解：从 GaN 到 InGaN 的转变，反之亦然，以谨慎的成分增量发生；每个增量对应于界面的一个单层，表明成核所需的时间比台阶的横向生长时间长。应变状态分析也通过将峰对分析应用于原子柱的位置来执行，以确定对比度的量化。应变映射产生的成分估计与从量化的 HAADF-STEM 获得的成分非常一致，尽管精度较低。讨论了提高应变映射精度的可能改进，为在原子尺度上量化任意四元合金开辟了潜在途径。