Wang Yu, Qiao Man, Li Yafei, Chen Zhongfang
Jiangsu Collaborative Innovation Centre of Biomedical Functional Materials, Jiangsu Key Laboratory of New Power Batteries, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China.
Nanoscale Horiz. 2018 May 1;3(3):327-334. doi: 10.1039/c7nh00091j. Epub 2018 Feb 1.
The prediction of new materials with peculiar topological properties is always desirable to achieve new properties and applications. In this work, by means of density functional theory computations, we extend the rule-breaking chemical bonding of planar pentacoordinate silicon (ppSi) into a periodic system: a C CaSi molecular building block containing a ppSi center is identified first, followed by the construction of an infinite CaSi monolayer, which is essentially a two-dimensional (2D) network of the CaSi motif. The moderate cohesive energy, absence of imaginary phonon modes, and good resistance to high temperature indicate that the CaSi monolayer is a thermodynamically and kinetically stable structure. In particular, a global minimum search reveals that the ppSi-containing CaSi monolayer is the lowest-energy structure in 2D space, indicating its great promise for experimental realization. The CaSi monolayer is a natural semiconductor with an indirect band gap of 0.5 eV, and it has rather strong optical absorption in the visible region of the solar spectrum. More interestingly, the unique atomic configuration endows the CaSi monolayer with an unusually negative Poisson's ratio. The rule-breaking geometric structure together with its exceptional properties makes the CaSi monolayer quite a promising candidate for applications in electronics, optoelectronics, and mechanics.
预测具有特殊拓扑性质的新材料一直是实现新特性和新应用的理想目标。在这项工作中，通过密度泛函理论计算，我们将平面五配位硅（ppSi）的非常规化学键扩展到一个周期性体系：首先确定了一个含有ppSi中心的C CaSi分子构建单元，随后构建了一个无限的CaSi单层，它本质上是CaSi motif的二维（2D）网络。适中的内聚能、不存在虚声子模式以及良好的耐高温性表明CaSi单层是一种热力学和动力学稳定的结构。特别地，全局最小搜索表明含ppSi的CaSi单层是二维空间中能量最低的结构，这表明它在实验实现方面具有很大的潜力。CaSi单层是一种间接带隙为0.5 eV的天然半导体，并且在太阳光谱的可见光区域具有相当强的光吸收。更有趣的是，独特的原子构型赋予CaSi单层异常负的泊松比。这种非常规的几何结构及其特殊性质使得CaSi单层成为电子学、光电子学和力学应用中非常有前途的候选材料。
