非晶硅中涌现的中程有序
Emergent medium-range order in amorphous silicon
AI总结：
本研究通过机器学习驱动的大规模原子模拟，揭示非晶硅中短程键合约束与长程原子排列相互作用，涌现出中程有序的立方、八面体对称模式，建立了第一尖锐衍射峰与中程有序实空间组织的直接联系。
摘要：
中程有序（MRO）是非晶材料的重要特征，但其原子排列的本质仍不明确。本文利用机器学习驱动的大规模非晶硅原子模拟，探究这种典型网络玻璃的中程有序。通过三维结构表征，我们发现中心原子周围的原子排列对称性随距离发生交叉：短距离处，结构由局部键合约束决定，从低密度非晶硅中占主导的四面体环境演变为极高密度非晶硅中高度配位且高度无序的局部环境；而在更长距离处，尽管短尺度不存在这些对称性，三维原子密度分布中却涌现出独特的立方和八面体对称模式。我们还发现，这种交叉伴随结构中拓扑环的准周期空间组织，环中心的特征间距与结构因子中第一尖锐衍射峰（FSDP）的长度尺度匹配，建立了该倒空间中程有序特征与其实空间组织的直接联系。这些结果表明，FSDP、环的空间相关性及涌现的取向对称性并非中程有序的独立表现，而是同一结构组织的不同方面。本研究为非晶硅的中程有序提供了统一的实空间图像，并指出网络玻璃的中程结构有序源于局部键合约束与高效堆积驱动的扩展原子排列的相互作用。
英文摘要：
Medium-range order (MRO) is an important feature of amorphous materials, but its nature in terms of atomic arrangement has remained elusive. Here, using large-scale machine-learning-driven atomistic simulations of amorphous silicon, we probe the MRO of this archetypal network glass. By characterizing the structure in three dimensions, we reveal that the symmetry of the atomic arrangement around a central atom shows a crossover as a function of distance. At short distances, the structure is determined by local bonding constraints, which evolve from predominantly tetrahedral environments in low-density amorphous silicon to highly coordinated and strongly disordered local environments in very-high-density amorphous silicon. At larger distances, however, distinct cubic- and octahedral-symmetry patterns emerge in the three-dimensional atomic-density distribution, despite the absence of these symmetries at shorter length scales. We find that this crossover is accompanied by a quasi-periodic spatial organization of the topological rings in the structure. The characteristic spacing between ring centers matches the length scale of the first sharp diffraction peak (FSDP) in the structure factor, establishing a direct connection between this reciprocal-space signature of MRO and its real-space organization. These results demonstrate that the FSDP, the spatial correlation of the rings, and emergent orientational symmetries are not independent manifestations of MRO, but reflect different aspects of a common structural organization. Our findings provide a unified real-space picture of MRO in amorphous silicon and suggest that intermediate-range structural order in network glasses emerges from the interplay between local bonding constraints and extended atomic arrangements driven by efficient packing.
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