In the present study we have combined in a same synchrotron x-ray experiment, reciprocal space map, multiwavelength anomalous diffraction and diffraction anomalous fine structure, to determine strain, crystallographic polarity, alloy composition and ordering at the atomic scale in [001]-oriented AlGaN nanowires grown by molecular beam epitaxy on GaN nanowire bases. The information that we obtain is averaged over a macroscopic ensemble of NWs. We find by diffraction anomalous fine structure an isotropic increased number of Ga-Ga pairs in the Ga next nearest coordination shell (cation sublattice) with respect to what is expected for the AlGaN alloy composition determined by anomalous diffraction. This significant deviation from random alloy atomic distribution is present whatever the AlN molar fraction and growth conditions. Our results are consistent with nanoscale composition fluctuations expected from both alloy disorder or kinematically driven spontaneous ordering, both effects being suspected to account for the physical properties of AlGaN ternary alloys.

中文翻译：

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AlGaN 纳米线成分波动的纳米级 X 射线研究

在本研究中，我们结合了同一个同步加速器 X 射线实验、倒易空间图、多波长异常衍射和衍射异常精细结构，以确定 [001] 取向的原子尺度上的应变、晶体极性、合金成分和有序性。通过分子束外延在 GaN 纳米线基底上生长的 AlGaN 纳米线。我们获得的信息在 NW 的宏观集合上进行了平均。我们通过衍射异常精细结构发现，相对于通过异常衍射确定的 AlGaN 合金成分的预期，在 Ga 下一个最近的配位壳（阳离子亚晶格）中各向同性增加的 Ga-Ga 对数量。无论 AlN 摩尔分数和生长条件如何，都存在这种与随机合金原子分布的显着偏差。