Wang Zhu-Jun, Dong Jichen, Li Linfei, Dong Guocai, Cui Yi, Yang Yang, Wei Wei, Blume Raoul, Li Qing, Wang Li, Xu Xiaozhi, Liu Kaihui, Barroo Cédric, Frenken Joost W M, Fu Qiang, Bao Xinhe, Schlögl Robert, Ding Feng, Willinger Marc-Georg
Scientific Center for Optical and Electron Microscopy, ETH Zürich , 8093 Zürich , Switzerland.
Department of Inorganic Chemistry , Fritz Haber Institute of the Max Planck Society , Berlin-Dahlem D-14195 , Germany.
ACS Nano. 2020 Feb 25;14(2):1902-1918. doi: 10.1021/acsnano.9b08221. Epub 2020 Feb 12.
Wafer-scale monocrystalline two-dimensional (2D) materials can theoretically be grown by seamless coalescence of individual domains into a large single crystal. Here we present a concise study of the coalescence behavior of crystalline 2D films using a combination of complementary methods. Direct observation of overlayer growth from the atomic to the millimeter scale and under model- and industrially relevant growth conditions reveals the influence of the film-substrate interaction on the crystallinity of the 2D film. In the case of weakly interacting substrates, the coalescence behavior is dictated by the inherent growth kinetics of the 2D film. It is shown that the merging of coaligned domains leads to a distinct modification of the growth dynamics through the formation of fast-growing high-energy edges. The latter can be traced down to a reduced kink-creation energy at the interface between well-aligned domains. In the case of strongly interacting substrates, the lattice mismatch between film and substrate induces a pronounced moiré corrugation that determines the growth and coalescence behavior. It furthermore imposes additional criteria for seamless coalescence and determines the structure of grain boundaries. The experimental findings, obtained here for the case of graphene, are confirmed by theory-based growth simulations and can be generalized to other 2D materials that show 3- or 6-fold symmetry. Based on the gained understanding of the relation between film-substrate interaction, shape evolution, and coalescence behavior, conditions for seamless coalescence and, thus, for the optimization of large-scale production of monocrystalline 2D materials are established.
理论上，通过将单个畴无缝合并成一个大的单晶，可以生长出晶圆级的单晶二维（2D）材料。在此，我们结合多种互补方法，对晶体二维薄膜的合并行为进行了简要研究。在模型相关和工业相关的生长条件下，从原子尺度到毫米尺度对覆盖层生长进行直接观察，揭示了薄膜-衬底相互作用对二维薄膜结晶度的影响。在弱相互作用衬底的情况下，合并行为由二维薄膜固有的生长动力学决定。结果表明，排列对齐的畴的合并通过形成快速生长的高能边缘，导致生长动力学发生显著改变。后者可追溯到排列良好的畴之间界面处扭结形成能量的降低。在强相互作用衬底的情况下，薄膜与衬底之间的晶格失配会引发明显的莫尔波纹，这决定了生长和合并行为。此外，它还对无缝合并提出了额外的标准，并决定了晶界的结构。本文针对石墨烯的实验结果，通过基于理论的生长模拟得到了证实，并且可以推广到其他具有三重或六重对称性的二维材料。基于对薄膜-衬底相互作用、形状演变和合并行为之间关系的理解，建立了无缝合并的条件，从而为优化单晶二维材料的大规模生产奠定了基础。
