Silicene on Ag(1 1 1): Geometric and electronic structures of a new honeycomb material of Si

IF 8.7 2区 工程技术 Q1 CHEMISTRY, PHYSICAL
Noriaki Takagi , Chun-Liang Lin , Kazuaki Kawahara , Emi Minamitani , Noriyuki Tsukahara , Maki Kawai , Ryuichi Arafune
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引用次数: 55

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 4×4,13×13R13.9°,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 3pz 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.

银上硅烯(1 1 1):一种新型硅蜂窝材料的几何和电子结构
硅烯是一种由硅原子组成的二维蜂窝片,由于其狄拉克费米子特征与自旋轨道耦合的结合而获得了许多令人着迷的特性,因此作为一种新的低维材料受到了广泛的关注。量子自旋霍尔效应和与现有硅器件技术的兼容性等新特性加剧了实现硅烯的竞争。本文利用扫描隧道显微成像(STM)、低能电子衍射(LEED)和密度泛函理论(DFT)等方法研究了生长在Ag(11 11)上的硅烯的几何和电子结构。Ag(11 11)上的硅烯呈局部屈曲结构,其中硅原子垂直于基面上移位。因此,出现了4×4、13×13R13.9°、4/3×4/3等几个上层建筑。通过STM, DFT计算和LEED动力学分析确定了4 × 4硅烯的原子排列,而其他超结构仍有待完全解析。在4 × 4硅烯中,Si原子排列成屈曲蜂窝结构,其中单元胞中18个Si原子中的6个Si原子垂直移位。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存在不可忽略的耦合。界面耦合显著改变了4 × 4硅烯的电子结构。垂直于样品表面施加磁场的扫描隧道光谱(STS)未观察到朗道能级序列。DFT计算表明,Si 3pz的π和π *能带与Ag电子态杂化,导致能带结构发生了剧烈的变化,从而导致狄拉克费米子特征的缺失以及电子态的二维化。这些发现表明,界面处的强耦合导致4 × 4硅烯的对称性破缺,从而导致狄拉克费米子特征的消失。对其它上部结构的几何结构和电子结构也进行了讨论。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Progress in Surface Science
Progress in Surface Science 工程技术-物理:凝聚态物理
CiteScore
11.30
自引率
0.00%
发文量
10
审稿时长
3 months
期刊介绍: Progress in Surface Science publishes progress reports and review articles by invited authors of international stature. The papers are aimed at surface scientists and cover various aspects of surface science. Papers in the new section Progress Highlights, are more concise and general at the same time, and are aimed at all scientists. Because of the transdisciplinary nature of surface science, topics are chosen for their timeliness from across the wide spectrum of scientific and engineering subjects. The journal strives to promote the exchange of ideas between surface scientists in the various areas. Authors are encouraged to write articles that are of relevance and interest to both established surface scientists and newcomers in the field.
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