Directing the Structure of Two-Dimensional Silica and Silicates
Directing the Structure of Two-Dimensional Silica and Silicates
复制标题
DOI：
10.1021/acs.jpcc.6b07008
复制
发表时间：
2016-12-01
影响因子：
3.7
通讯作者：
Altman, Eric I.
中科院分区：
文献类型：
--
作者：
Malashevich, Andrei;Ismail-Beigi, Sohrab;Altman, Eric I.
密度泛函理论被用来评估的可行性的方法来控制最近发现的二维形式的二氧化硅的结构。在雅阁与以前的工作，六元环中的角共享SiO 4四面体的镜像平面的六边形双层仅产生比a-石英稍高的能量。包括四到八元环的结构进行了评估，并在某些情况下，发现低至17毫电子伏/硅高能量比六方双层。当施加双轴或单轴拉伸应变时，八元环、六元环和四元环的组合变得有利，因为具有较大环的结构的密度较低。这些发现，连同实验，揭示了膨胀的二氧化硅双层匹配的金属基板的晶格，表明外延应变可用于控制的双层结构。还研究了用Ge和Al作为原型四价和三价掺杂剂替代Si。取代锗硅是积极不利的，并提供了没有明显的优势，结构控制纯二氧化硅双层。相比之下，铝取代是积极有利的，只有最低限度地扭曲的双层。结果发现，虽然六方双层仍然有利，但伴随每个Al的骨架外电子供体K和H在可能的情况下更喜欢占据更大的环，从而迫使Al也驻留在大环中。这表明，双层结构可以通过用Si取代三价掺杂剂和选择有利于较大环的骨架外电子供体来控制。
Density functional theory was used to assess the viability of approaches to controlling the structure of a recently discovered two-dimensional form of SiO2. In accord with prior work, a hexagonal bilayer of mirror image planes of corner sharing SiO4 tetrahedra in six-membered rings yielded only a slightly higher energy than a-quartz. Structures including four through eight-membered rings were evaluated and in certain cases found to be as little as 17 meV/Si higher in energy than the hexagonal bilayer. When either biaxial or uniaxial tensile strain was applied, combinations of eight-, six-, and four-membered rings became favored due to the lower density of structures with larger rings. These findings, together with experiments that reveal expansion of silica bilayers to match the lattice of metal substrates, suggest that epitaxial strain may be used to control the bilayer structure. Replacement of Si with Ge and Al as prototypical tetravalent and trivalent dopants was also investigated. Substituting Ge for Si was energetically unfavorable and offered no obvious advantage for structural control over pure SiO2 bilayers. In contrast, Al substitution was energetically favorable and only minimally distorted the bilayer. It was found that while the hexagonal bilayer remained favored, the extra-framework electron donors K and H that accompany each Al preferred to occupy larger rings when possible, thus forcing Al to reside in large rings as well. This suggests that the bilayer structure may be controlled through substitution of Si for trivalent dopants and selection of extra-framework electron donors that favor larger rings.