Bonding, structure, and mechanical stability of 2D materials: the predictive power of the periodic table,Nanoscale Horizons

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Bonding, structure, and mechanical stability of 2D materials: the predictive power of the periodic table
Nanoscale Horizons ( IF 8.0 ) Pub Date : 2021-09-08 , DOI: 10.1039/d1nh00113b
Peter Hess ₁

Affiliation

This tutorial review describes the ongoing effort to convert main-group elements of the periodic table and their combinations into stable 2D materials, which is sometimes called modern ‘alchemy’. Theory is successfully approaching this goal, whereas experimental verification is lagging far behind in the synergistic interplay between theory and experiment. The data collected here gives a clear picture of the bonding, structure, and mechanical performance of the main-group elements and their binary compounds. This ranges from group II elements, with two valence electrons, to group VI elements with six valence electrons, which form not only 1D structures but also, owing to their variable oxidation states, low-symmetry 2D networks. Outside of these main groups reviewed here, predominantly ionic bonding may be observed, for example in group II–VII compounds. Besides high-symmetry graphene with its shortest and strongest bonds and outstanding mechanical properties, low-symmetry 2D structures such as various borophene and tellurene phases with intriguing properties are receiving increasing attention. The comprehensive discussion of data also includes bonding and structure of few-layer assemblies, because the electronic properties, e.g., the band gap, of these heterostructures vary with interlayer layer separation and interaction energy. The available data allows the identification of general relationships between bonding, structure, and mechanical stability. This enables the extraction of periodic trends and fundamental rules governing the 2D world, which help to clear up deviating results and to estimate unknown properties. For example, the observed change of the bond length by a factor of two alters the cohesive energy by a factor of four and the extremely sensitive Young's modulus and ultimate strength by more than a factor of 60. Since the stiffness and strength decrease with increasing atom size on going down the columns of the periodic table, it is important to look for suitable allotropes of elements and binaries in the upper rows of the periodic table when mechanical stability and robustness are issues. On the other hand, the heavy compounds are of particular interest because of their low-symmetry structures with exotic electronic properties.

中文翻译：

二维材料的键合、结构和机械稳定性：元素周期表的预测能力

本教程回顾描述了将元素周期表的主族元素及其组合转换为稳定的 2D 材料的持续努力，这有时被称为现代“炼金术”。理论正在成功地接近这个目标，而实验验证在理论与实验之间的协同相互作用方面远远落后。此处收集的数据清楚地显示了主族元素及其二元化合物的键合、结构和机械性能。这范围从具有两个价电子的 II 族元素到具有六个价电子的 VI 族元素，它们不仅形成一维结构，而且由于其可变的氧化态，还形成了低对称性的二维网络。在此处审查的这些主要群体之外，可能会观察到主要的离子键合，例如在第 II-VII 组化合物中。除了具有最短和最强键和出色机械性能的高对称性石墨烯外，低对称性二维结构（例如各种硼烯和碲烯相）也越来越受到关注。数据的综合讨论还包括少层组件的键合和结构，因为电子特性，例如，这些异质结构的带隙随层间层间距和相互作用能而变化。可用数据允许识别键合、结构和机械稳定性之间的一般关系。这使得能够提取控制 2D 世界的周期性趋势和基本规则，这有助于清除偏差结果并估计未知属性。例如，观察到的键长变化两倍，内聚能变化四倍，极其敏感的杨氏模量和极限强度变化超过 60 倍。因为刚度和强度随着原子的增加而降低尺寸在元素周期表的列中向下移动，当机械稳定性和鲁棒性成为问题时，重要的是要在元素周期表的上排寻找合适的元素和二元同素异形体。另一方面，重化合物因其具有奇特电子特性的低对称结构而受到特别关注。

更新日期：2021-09-08

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