Nanoassembly Growth Model for Subdomain and Grain Boundary Formation in 1T′ Layered ReS2

Grain boundaries (GBs) significantly affect the electrical, optical, magnetic, and mechanical properties of 2D materials. An anisotropic 2D material like ReS2 provides unprecedented opportunities to explore novel GB properties, since the reduced lattice symmetry offers greater degrees of freedom to build new GB structures. Here the atomic structure and formation mechanism of unusual multidomain and diverse GB structures in the vapor phase synthesized ReS2 atomic layers are reported. Using high-resolution electron microscopy, two major categories of GBs are observed in each ReS2 domain, namely, the joint GB including three structures, and the GBs formed from a reconstruction of Re4-chains including seven different structures. Based on the experimental observations, a novel "nanoassembly growth model" is proposed to elucidate the growth process of ReS2, where three types of Re4-chain reconstruction give rise to a multidomain structure. Moreover, it is shown that by controlling the thermodynamics of the growth process, the structure and density of GB in the ReS2 domain can be tailored. First-principles calculations point to interesting new properties resulting from such GBs, such as a new electron state or ferromagnetism, which are highly sought after in the construction of novel 2D devices.