Spatial Control of Substitutional Dopants in Hexagonal Monolayer WS₂: The Effect of Edge Termination

The ability of controlling density and spatial distribution of substitutional dopants in semiconductors is crucial for achieving desired physicochemical properties. Substitutional doping with adjustable doping levels has been previously demonstrated in two-dimensional (2D) transition metal dichalcogenides (TMDs); however, the micron spatial control of dopant distribution remains an open field. In this work, we demonstrate that edge termination is an important characteristic of 2D TMD monocrystals that affects the distribution of substitutional dopants. Particularly, in chemical vapor deposition (CVD)-grown monolayer WS₂, we find that a higher density of transition metal dopants is always incorporated in S-terminated domains when compared to W-terminated domains. Two representative examples demonstrate this sub-micron spatial distribution control, including hexagonal Fe- and V-doped WS₂ monolayers. Density functional theory (DFT) calculations are further performed, indicating that the edge-dependent dopant distribution is due to a strong binding of W atoms at W-zigzag edges, resulting in the formation of open sites at S-zigzag edges that enable preferential dopant incorporation. Based on our results, we envision that edge termination in crystalline TMD monolayers can be utilized as a novel and effective knob for engineering the spatial distribution of substitutional dopants, leading to in-plane hetero-/multi-junctions that could display fascinating electronic, optoelectronic, and magnetic properties.