Antiphase boundaries (APBs) are special grain boundaries with especially low interfacial energy and high degree of symmetry. In two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), APBs have attracted broad interests as one-dimensional metallic wire embedded in a semiconducting matrix [1-3]. Previously, APBs in a 2D system have nanometer-scale facets with kinks, which induce huge changes to the electronic properties [4]. Herein, we investigated the anisotropic features of APBs (i.e., straight and saw-toothed APBs) and their different electron transport behaviors.
In this study, representative 2H phase TMDs (e.g., WS2 and MoS2) synthesized by chemical vapor deposition method were used. To produce APBs dominantly through van der Waals epitaxial growth, TMD flakes were directly grown on a pristine graphene template [5]. We observed that the chalcogen-facing and transition-metal-facing APBs have straight and saw-toothed overall structures, respectively. The combined experimental and computational results demonstrate that the anisotropy of APBs is attributed to having an energetically stable atomic configurations, consisting of under- and over-coordinated chalcogen atoms. Current image using conductive atomic force microscopy shows that both types of APBs behaves like the conductive wires predicted in previous studies [1,3], but the electron transport behavior obtained from two-probe field effect transistor represents markedly reduced electron mobility in saw-toothed APBs. It indicates that the lots of kinks in saw-toothed APBs could be the main cause of electron scattering.
In conclusion, we offer dedicated understanding of the anisotropy of the APB line defect, which could not be predicted using theoretical models, and the effect of the anisotropic features on the electronic transport behavior. Our results thus reveal crucial insight into microstructure-related electronic transport property and could extend the applications of 2D materials with desirable properties through defect engineering.
