摘要
相第四主族单硫化合物(γ-MX)是理论预测出的一种全新的具有半导体特性的稳定结构.最近,人们通过化学气相沉积法成功合成了相关材料,但样品却表现出金属性.生长过程引入的拓扑缺陷无处不在,可能会对材料电子行为带来重要影响.但是,关于这些拓扑缺陷的结构和性质的研究仍未开展.以γ相GeSe为例,我们通过第一性原理计算系统研究了其位错核和晶界的结构、热力学和电子性质.结果发现,不同的原子排布方式可以形成多样的衍生位错核.基于最低能量的位错核,我们研究了晶界结构随着倾斜角的变化,并特别构建了全部可能的60°孪生晶界,发现它们具有独特的六边形结构或Ge–Ge键.进一步地,针对能量最低的21.8°和60°晶界的电子结构分析发现,大多数晶界体态和缺陷态之间具有共振作用,这使得体系表现出金属性质;而某些结构则仍表现半导体性,但带隙显著减小.这些电子性质在其他γ-MX中也普遍存在.不同晶界的扫描隧道显微镜图像展现出特征性图案,可以作为表征它们的手段.我们的结果表明,应对γ-MX中具有多样性质的拓扑缺陷进行有目的的设计以促进其潜在应用.
γ-Phase group Ⅳ monochalcogenides(γ-MX),predicted to be stable with semiconducting characteristics,have been synthesized by chemical vapor deposition but showing metallicity. The ubiquitous topological defects introduced during the growth process could bring about key influences on the electronic behaviors, but their structures and properties remain unexplored. Taking monolayer γ-GeSe as an example, first-principles calculations were performed to investigate the structural, thermodynamic, and electronic properties of dislocation cores(DCs) and grain boundaries(GBs). Various derivative DCs emerge depending on different arrangements of atoms. The calculated low-energy DCs are then used to determine preferential structures of GBs versus tilt angle, with special attention paid to the whole family of 60°twin GBs, showing distinct hexagons or Ge–Ge bonds. Furthermore, electronic structures are calculated for thermodynamically favored 21.8° with closely packed dislocations and60° twin GBs. Most of them show a strong resonance between the bulk and dislocation states, rendering the systems metallic,while some display semiconducting behaviors with reduced band gap. These electronic properties are universal for otherγ-MXs. The simulated scanning tunneling microscopy images show characteristic fingerprints to help identify their existence in practice. Our results show that topological defects in γ-MX with versatile properties should be carefully engineered for their potential applications.
作者
曾圣锋
邹小龙
Shengfeng Zeng;Xiaolong Zou(Shenzhen Geim Graphene Center,Tsinghua-Berkeley Shenzhen Institute and Tsinghua Shenzhen International Graduate School,Tsinghua University,Shenzhen 518055,China)
基金
supported by the National Natural Science Foundation of China(11974197 and 51920105002)
Guangdong Innovative and Entrepreneurial Research Team Program(2017ZT07C341)
the Bureau of Industry and Information Technology of Shenzhen for the 2017 Graphene Manufacturing Innovation Center Project(201901171523).
