Zhao Chunxiang, Cai Xiaolin, Liu Xilai, Wang Junfei, Chen Weiguang, Zhang Liying, Zhang Yinuo, Zhu Zhili, Liu Chengyan, Niu Chunyao, Jia Yu
International Laboratory for Quantum Functional Materials of Henan, and School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450001, China.
Key Laboratory for Special Functional Materials of Ministry of Education, and School of Material Science and Engineering, Henan University, Kaifeng 475004, China.
Phys Chem Chem Phys. 2022 Mar 23;24(12):7512-7520. doi: 10.1039/d2cp00070a.
Elemental two-dimensional (2D) materials have attracted extraordinary interest compared with other 2D materials over the past few years. Fifteen elements from group IIIA to VIA have been discussed experimentally or theoretically for the formation of 2D monolayers, and the remaining few elements still need to be identified. Here, using first-principles calculations within density functional theory (DFT) and molecular dynamics simulations (AIMDs), we demonstrated that polonium can form stable 2D monolayers (MLs) with a 1T-MoS-like structure. The band structure calculations revealed that polonium monolayers possess strong semiconducting properties with a band gap of ∼0.9 eV, and such semiconducting properties can well sustain up to a thickness of 4 MLs with a bandgap of ∼0.1 eV. We also found that polonium monolayers can be achieved through a spontaneous phase transition of ultrathin films with magic thicknesses, resulting in a weaker van der Waals interaction of ∼32 meV Å between each three atomic layers. Also, the underlying physics comes from layered Peierls-like distortion driven by strong quantum size effects. Based on these intriguing findings, a suitable substrate on which the polonium monolayer can be grown through an epitaxial growth technique is proposed for further experiments. Our work not only extends completely the puzzle of elemental 2D monolayer materials from group IIIA to VIA, but also presents a new formation mechanism of 2D materials beyond the database of bulk materials with layered van der Waals interactions.
在过去几年中，与其他二维材料相比，单质二维（2D）材料引起了人们极大的兴趣。从IIIA族到VIA族的15种元素已在实验或理论上被讨论用于形成二维单原子层，其余少数元素仍有待确定。在此，我们使用密度泛函理论（DFT）中的第一性原理计算和分子动力学模拟（AIMD），证明钋可以形成具有类1T-MoS结构的稳定二维单原子层（MLs）。能带结构计算表明，钋单原子层具有强半导体性质，带隙约为0.9 eV，并且这种半导体性质在厚度达到4个单原子层时仍能很好地维持，带隙约为0.1 eV。我们还发现，钋单原子层可以通过具有神奇厚度的超薄膜的自发相变来实现，导致每三个原子层之间的范德华相互作用较弱，约为32 meV Å。此外，其背后的物理原理来自于由强量子尺寸效应驱动的层状类佩尔斯畸变。基于这些有趣的发现，我们提出了一种合适的衬底，钋单原子层可以通过外延生长技术在其上生长，以供进一步实验。我们的工作不仅完全扩展了从IIIA族到VIA族的单质二维单原子层材料的谜题，还提出了一种超越具有层状范德华相互作用的体材料数据库的二维材料新形成机制。
