‘Colorful’ Polyline Grain Boundaries in Two-dimensional Transition Metal Dichalcogenides

Abstract

Grain boundaries (GBs) are vital to crystal materials and their applications. Although the GBs in bulk and two-dimensional materials have been extensively studied, the polyline GBs prevalently forming in transition metal dichalcogenide monolayers by a sequence of folded segments remain a mystery. We visualize the large-area distribution of the polyline GBs in MoSe2 monolayers by means of a strain mapping method and unravel their structural origin using ab initio calculations combined with high-resolution atomic characterizations. Unlike normal GBs in two-dimensional materials with one type of dislocation cores, the polyline GBs consist of two basic elements—4|8 and 4|4|8 cores, whose alloying results in structural diversity and distinctly high stability due to relieved stress fields nearby. The defective polygons can uniquely migrate along the polyline GBs via the movement of single molybdenum atoms, unobtrusively giving the GBs their chameleon-like ‘colorful’ appearances. Furthermore, the polyline GBs can achieve useful functionalities such as intrinsic magnetism and highly active electrocatalysis.