Abstract Silicene, a two-dimensional honeycomb sheet consisting of Si atoms, has attracted much attention as a new low-dimensional material because it gains various fascinating characteristics originating from the combination of Dirac fermion features with spin–orbit coupling. The novel properties such as the quantum spin Hall effect and the compatibility with the current Si device technologies have fueled competition to realize the silicene. This review article focuses on the geometric and electronic structures of silicene grown on Ag(1 1 1) investigated by scanning tunneling microcopy (STM), low energy electron diffraction (LEED) and density functional theory (DFT) calculations. The silicene on Ag(1 1 1) takes locally-buckled structure in which the Si atoms are displaced perpendicularly to the basal plane. As a result, several superstructures such as 4 × 4 , 13 × 13 R 13.9 ° , 4 / 3 × 4 / 3 , and etc. emerge. The atomic arrangement of the 4 × 4 silicene has been determined by STM, DFT calculations and LEED dynamical analysis, while the other superstructures remain to be fully-resolved. In the 4 × 4 silicene, Si atoms are arranged to form a buckled honeycomb structure where six Si atoms of 18 Si atoms in the unit cell are displaced vertically. The displacements lead to the vertical shift of the substrate Ag atoms, indicating the non-negligible coupling at the interface between the silicene layer and the substrate. The interface coupling significantly modifies the electronic structure of the 4 × 4 silicene. No Landau level sequences were observed by scanning tunneling spectroscopy (STS) with magnetic fields applied perpendicularly to the sample surface. The DFT calculations showed that the π and π ∗ bands derived from the Si 3p z are hybridized with the Ag electronic states, leading to the drastic modification in the band structure and then the absence of Dirac fermion features together with the two-dimensionality in the electronic states. These findings demonstrate that the strong coupling at the interface causes the symmetry breaking for the 4 × 4 silicene and as a result the disappearance of Dirac fermion features. The geometric and electronic structures of other superstructures are also discussed.

中文翻译：

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硅基 Ag(111)：一种新型蜂窝状硅材料的几何和电子结构

摘要 硅烯是一种由硅原子组成的二维蜂窝状薄片，由于狄拉克费米子特征与自旋轨道耦合的结合，获得了各种迷人的特性，作为一种新型低维材料而备受关注。量子自旋霍尔效应等新特性以及与当前 Si 器件技术的兼容性推动了实现硅烯的竞争。这篇综述文章侧重于通过扫描隧道显微镜 (STM)、低能电子衍射 (LEED) 和密度泛函理论 (DFT) 计算研究在 Ag(1 1 1) 上生长的硅烯的几何和电子结构。Ag(1 1 1) 上的硅烯采用局部屈曲结构，其中硅原子垂直于基面位移。因此，出现了4×4、13×13 R 13.9°、4 / 3 × 4 / 3 等几种上层建筑。4 × 4 硅烯的原子排列已通过 STM、DFT 计算和 LEED 动力学分析确定，而其他超结构仍有待完全解析。在 4×4 硅烯中，Si 原子排列形成屈曲蜂窝结构，其中晶胞中 18 个 Si 原子中的 6 个 Si 原子垂直位移。位移导致衬底银原子的垂直位移，表明在硅烯层和衬底之间的界面处不可忽略的耦合。界面耦合显着改变了 4×4 硅烯的电子结构。通过将磁场垂直施加到样品表面的扫描隧道光谱 (STS) 没有观察到朗道能级序列。DFT 计算表明，源自 Si 3p z 的 π 和 π * 能带与 Ag 电子态杂化，导致能带结构发生剧烈变化，然后狄拉克费米子特征的缺失以及二维电子状态。这些发现表明，界面处的强耦合导致 4 × 4 硅烯的对称性破坏，从而导致狄拉克费米子特征的消失。还讨论了其他超结构的几何和电子结构。这些发现表明，界面处的强耦合导致 4 × 4 硅烯的对称性破坏，从而导致狄拉克费米子特征的消失。还讨论了其他超结构的几何和电子结构。这些发现表明，界面处的强耦合导致 4 × 4 硅烯的对称性破坏，从而导致狄拉克费米子特征的消失。还讨论了其他超结构的几何和电子结构。