Material Research Institute, ‡2-Dimensional Crystal Consortium, §Department of Physics, ∥Department of Chemistry, and ⊥Department of Materials Science and Engineering, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
Nano Lett. 2017 Sep 13;17(9):5297-5303. doi: 10.1021/acs.nanolett.7b01641. Epub 2017 Aug 28.
Grain boundaries in two-dimensional crystals are usually thought to separate distinct crystallites and as such they must either form closed loops or terminate at the boundary of a sample. However, when an atomically thin two-dimensional crystal grows on a substrate of nonzero Gaussian curvature, it can develop finite-length grain boundaries that terminate abruptly within a monocrystalline domain. We show that by properly designing the substrate topography, these grain boundaries can be placed at desired locations and at specified misfit angles, as the thermodynamic ground state of a two-dimensional (2D) system bound to a substrate. Compared against the hypothetical competition of growing defectless 2D materials on a Gaussian-curved substrate with consequential fold development or detachment from the substrate, the nucleation and formation of finite-length grain boundaries can be made energetically favorably given sufficient substrate adhesion on the order of tens of meV/Å for typical 2D materials. New properties specific to certain grain boundary geometries, including magnetism and metallicity, can thus be engineered into 2D crystals through topographic design of their substrates.
二维晶体中的晶界通常被认为是分隔不同晶粒的界面，因此它们必须形成封闭的环，或者在样品的边界处终止。然而，当原子层厚的二维晶体在具有非零高斯曲率的衬底上生长时，它可以在单晶区内形成具有有限长度的晶界，这些晶界会突然终止。我们表明，通过适当设计衬底的形貌，可以将这些晶界放置在所需的位置和指定的失配角处，这是二维（2D）系统结合到衬底时的热力学基态。与在具有褶皱发展或从衬底脱离的高斯弯曲衬底上生长无缺陷 2D 材料的假设竞争相比，对于典型的 2D 材料，只要衬底的附着力达到数十毫伏/埃的量级，就可以使有限长度晶界的成核和形成在能量上变得有利。通过对衬底的形貌进行设计，可以将特定晶界几何形状所具有的新特性（包括磁性和金属性）引入到 2D 晶体中。
