Department of Mechanical Engineering and Materials Science, Department of Chemistry, and the Smalley Institute for Nanoscale Science and Technology, Rice University , Houston, Texas 77005, United States.
ACS Nano. 2013 Dec 23;7(12):10475-81. doi: 10.1021/nn4052887. Epub 2013 Nov 19.
Grain boundaries (GBs) are structural imperfections that typically degrade the performance of materials. Here we show that dislocations and GBs in two-dimensional (2D) metal dichalcogenides MX2 (M = Mo, W; X = S, Se) can actually improve the material by giving it a qualitatively new physical property: magnetism. The dislocations studied all display a substantial magnetic moment of ∼1 Bohr magneton. In contrast, dislocations in other well-studied 2D materials are typically nonmagnetic. GBs composed of pentagon-heptagon pairs interact ferromagnetically and transition from semiconductor to half-metal or metal as a function of tilt angle and/or doping level. When the tilt angle exceeds 47°, the structural energetics favor square-octagon pairs and the GB becomes an antiferromagnetic semiconductor. These exceptional magnetic properties arise from interplay of dislocation-induced localized states, doping, and locally unbalanced stoichiometry. Purposeful engineering of topological GBs may be able to convert MX2 into a promising 2D magnetic semiconductor.
晶界（GBs）是结构上的缺陷，通常会降低材料的性能。在这里，我们表明二维（2D）金属二卤化物 MX2（M = Mo，W；X = S，Se）中的位错和晶界实际上可以通过赋予其一种全新的物理性质来改善材料：磁性。所研究的位错都显示出约 1 玻尔磁子的大量磁矩。相比之下，其他经过充分研究的二维材料中的位错通常是非磁性的。由五边形-七边形对组成的晶界呈铁磁相互作用，并随着倾斜角和/或掺杂水平的变化，从半导体转变为半金属或金属。当倾斜角超过 47°时，结构能态有利于正方形-八边形对，晶界成为反铁磁半导体。这些特殊的磁性性质源于位错诱导的局域态、掺杂和局部非化学计量比的相互作用。拓扑晶界的有目的工程设计可能能够将 MX2 转化为一种有前途的二维磁性半导体。
