Nakayama Koji S, Nishijima Masahiko, Zhang Yicheng, Inoue Koji, Chen Chuantong, Ueshima Minoru, Suganuma Katsuaki
The Institute of Scientific and Industrial Research, The University of Osaka, 8-1 Mihogaoka, Ibaraki, 567-0047, Osaka, Japan.
International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, 2145-2, Oarai, Ibaraki, 311-1313, Japan.
Sci Rep. 2025 Aug 27;15(1):31539. doi: 10.1038/s41598-025-15737-8.
The atomic structure of amorphous Si (a-Si) has traditionally been described by the continuous random network (CRN) model, which consists of the four-coordinated Si with a non-periodic structure. However, the paracrystalline model, consisting of strained nanocrystals embedded within a disordered matrix, has gained traction. This shift is largely driven by fluctuation electron microscopy observations, which reveal the distinct diffraction patterns that are inconsistent with the CRN model. However, the degree and nature of paracrystallinity remain unclear due to a lack of experimental approaches capable of revealing finite size effects. In this paper, we present the atomic structure of a-Si that appeared in a liquid quenched Ag-Si alloy. Fast Fourier transform and electron diffraction patterns exhibit excellent agreement with molecular dynamics simulations. Furthermore, nano-beam electron diffraction reveals distinct diffraction spots that support the paracrystalline model. Importantly, these diffraction spots violate the conventional crystallographic extinction rule, implying symmetry breaking within the paracrystalline structure. This is significant because the appearance of forbidden reflections offers direct evidence of local structural changes and provides new insight into the underlying disorder in a-Si.
非晶硅（a-Si）的原子结构传统上是用连续随机网络（CRN）模型来描述的，该模型由具有非周期性结构的四配位硅组成。然而，由嵌入无序基体中的应变纳米晶体组成的准晶模型越来越受到关注。这种转变主要是由波动电子显微镜观察推动的，这些观察揭示了与CRN模型不一致的独特衍射图案。然而，由于缺乏能够揭示有限尺寸效应的实验方法，准晶度的程度和性质仍不清楚。在本文中，我们展示了出现在液体淬火Ag-Si合金中的a-Si的原子结构。快速傅里叶变换和电子衍射图案与分子动力学模拟表现出极好的一致性。此外，纳米束电子衍射揭示了支持准晶模型的独特衍射斑点。重要的是，这些衍射斑点违反了传统的晶体消光规则，这意味着准晶结构内的对称性破缺。这很重要，因为禁戒反射的出现提供了局部结构变化的直接证据，并为准晶结构中潜在的无序提供了新的见解。
