Department of Chemistry and Materials Chemistry Centre, Christopher Ingold Laboratory, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom.
J Phys Chem B. 2011 Dec 8;115(48):14246-55. doi: 10.1021/jp205090s. Epub 2011 Aug 17.
We studied the low-frequency Raman and X-ray scattering behavior of amorphous silicon (a-Si) at high pressure throughout the range where the density-driven polyamorphic transformation between the low-density amorphous (LDA) semiconductor and a novel metallic high-density amorphous (HDA) polyamorph occurs. The experimental data were analyzed with the aid of molecular dynamics (MD) simulations using the Stillinger-Weber potential. The heat capacity of a-Si obtained from the low pressure Raman data exhibits non Debye-like behavior, but the effect is small, and our data support the conclusion that no boson peak is present. The high-pressure Raman data show the presence of a distinct low frequency band for the HDA polyamorph in agreement with ab initio MD simulations. Spatially resolved synchrotron X-ray diffraction was used to study the high pressure behavior of the a-Si sample throughout the LDA-HDA transition range without interference by crystallization events. The X-ray data were analyzed using an iterative refinement strategy to extract real-space structural information. The appearance of the first diffraction peak (FDP) in the scattering function S(Q) is discussed in terms of the void structure determined from Voronoi analysis of the MD simulation data.
我们研究了非晶硅（a-Si）在低密度非晶（LDA）半导体和新型金属高密度非晶（HDA）多晶之间的密度驱动多晶转变范围内的低频 Raman 和 X 射线散射行为。借助分子动力学（MD）模拟，使用 Stillinger-Weber 势对实验数据进行了分析。从低压 Raman 数据得出的 a-Si 热容表现出非德拜行为，但影响很小，我们的数据支持不存在玻色峰的结论。高压 Raman 数据显示 HDA 多晶存在明显的低频带，与从头算 MD 模拟结果一致。同步加速器 X 射线衍射用于在没有结晶事件干扰的情况下研究整个 LDA-HDA 转变范围内的 a-Si 样品的高压行为。使用迭代细化策略分析 X 射线数据，以提取实空间结构信息。根据 Voronoi 分析 MD 模拟数据确定的空隙结构，讨论散射函数 S(Q)中的第一个衍射峰（FDP）的出现。
