Fig. 3. Growth mechanism of the WS₂ quantum well in WSe₂.

Atomic models of (A) 5|7 dislocation at the WS₂/WSe₂ interface due to lattice mismatch, (B) dislocation climbs one unit cell into WSe₂ by inserting a W atom and an S₂ pair, (C) substitution of Se by S in pentagon of the 5|7 dislocation, and (D) subsequent substitution of Se atoms next to the 5|7 dislocation by S resulting in a four–unit cell–wide WS₂ nanoseed. (E) Energy barrier for S_Se substitution under different levels of compressive strain. (F) Strain mapping based on bond length analysis for the atomic model in (B). See Materials and Methods for details. The green dashed line indicates the WS₂/WSe₂ interface. (G) Structural model showing a short WS₂ strip four unit cells wide and six unit cells long after repeating the insertion-substitution process six times.