Miscut surfaces of layered crystals can exhibit a stair-like sequence of terraces having periodic variation in their atomic structure. For hexagonal close-packed and related crystal structures with an $\alpha \beta \alpha \beta$ stacking sequence, there have been long-standing questions regarding how the differences in adatom attachment kinetics at the steps separating the terraces affect the fractional coverage of $\alpha$ versus $\beta$ termination during crystal growth. To demonstrate how surface x-ray scattering can help address these questions, we develop a general theory for the intensity distributions along crystal truncation rods (CTRs) for miscut surfaces with a combination of two terminations. We consider half-unit-cell-height steps, and variation of the coverages of the terraces above each step. Example calculations are presented for the GaN $\left(0001\right)$ surface with various reconstructions. These show which CTR positions are most sensitive to the fractional coverage of the two terminations. We compare the CTR profiles for exactly oriented surfaces to those for vicinal surfaces having a small miscut angle, and investigate the circumstances under which the CTR profile for an exactly oriented surface is equal to the sum of the intensities of the corresponding family of CTRs for a miscut surface.

中文翻译：

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来自错切表面的晶体截断杆，带有交替的端接

层状晶体的错切表面会呈现出阶梯状的梯田序列，梯阶的原子结构会周期性变化。对于六方密堆积和相关的晶体结构，具有$\alpha \beta \alpha \beta$ 堆积顺序方面，存在长期存在的问题，即在分离梯阶的步骤中，原子附着动力学的差异如何影响部分覆盖率。 $\alpha$ 相对 $\beta$在晶体生长过程中终止。为了说明表面X射线散射如何帮助解决这些问题，我们针对具有两个终端的错切表面沿晶体截断棒（CTR）的强度分布开发了一个通用理论。我们考虑单元格高度的半个步骤，以及每个步骤上方露台覆盖率的变化。给出了GaN的示例计算$（0001）$表面进行各种重建。这些表明哪个CTR位置对两个终端的部分覆盖范围最敏感。我们将精确定向表面的CTR轮廓与误切角较小的邻近表面的CTR轮廓进行比较，并研究在精确定向表面的CTR轮廓等于相应CTR系列强度的总和的情况。错切的表面。