State Key Laboratory of Mechanics and Control of Mechanical Structures, Key Laboratory for Intelligent Nano Materials and Devices of Ministry of Education, and Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China.
Department of Materials Science and NanoEngineering and Department of Chemistry, Rice University, Houston, TX 77005, USA.
Sci Adv. 2019 Sep 27;5(9):eaax0246. doi: 10.1126/sciadv.aax0246. eCollection 2019 Sep.
Two-dimensional boron, borophene, was realized in recent experiments but still lacks an adequate growth theory for guiding its controlled synthesis. Combining ab initio calculations and experimental characterization, we study edges and growth kinetics of borophene on Ag(111). In equilibrium, the borophene edges are distinctly reconstructed with exceptionally low energies, in contrast to those of other two-dimensional materials. Away from equilibrium, sequential docking of boron feeding species to the reconstructed edges tends to extend the given lattice out of numerous polymorphic structures. Furthermore, each edge can grow via multiple energy pathways of atomic row assembly due to variable boron-boron coordination. These pathways reveal different degrees of anisotropic growth kinetics, shaping borophene into diverse elongated hexagonal islands in agreement with experimental observations in terms of morphology as well as edge orientation and periodicity. These results further suggest that ultrathin borophene ribbons can be grown at low temperature and low boron chemical potential.
二维硼材料，即硼烯，最近在实验中得到了实现，但仍缺乏一种足够的生长理论来指导其可控合成。本研究结合了第一性原理计算和实验表征，研究了硼烯在 Ag(111)表面上的边缘和生长动力学。在平衡状态下，硼烯边缘表现出独特的低能重构，这与其他二维材料的边缘明显不同。在非平衡状态下，硼供体物种依次连接到重构边缘上，倾向于将给定的晶格扩展为多种多晶结构。此外，由于硼-硼配位的变化，每个边缘都可以通过多种原子行组装的能量途径进行生长。这些途径揭示了不同程度的各向异性生长动力学，使得硼烯形成了各种拉长的六边形岛，这与实验观察到的形态以及边缘取向和周期性一致。这些结果进一步表明，在低温和低硼化学势下可以生长出超薄的硼烯带。
